Updated Itinerary. Try again! 23 Days, Leaving October 29, England and Southern Wales.

Day 3: If you enjoy gardens you might consider the Lost Gardens of Heligan which is NE-ish from Falmouth. It might be kind of spendy for just a couple of hours, though. Since you are going to Eden Project you could also do it on that day. The person that restored the Lost Gardens of Heligan also started the Eden Project.

https://www.heligan.com/

Day 5: If the weather is nice you might consider taking the ferry across the Fal estuary to St Mawes and do the castle on that side of the river. IF the weather is pleasant in the AM, I might consider doing this first in case things get worse in the afternoon!

https://www.falriver.co.uk/getting-about/ferries/st-mawes-ferry

Day 6: I didn't go to Eden Project but did do a visit to Wheal Martin, a china clay pit museum.

https://www.wheal-martyn.com/

I agree with the comments about Liverpool. We were there in 2017 in May. I was at a conference, my wife did touring. There are a number of museums, which she toured and enjoyed - all free. The "ferry cross the Mersy to the land that I love" is fun. We took it, and got off in Birkenhead (across the river). There is a fascinating U-boat museum, which is inexpensive, and has many U-boat artifacts (full medical kit, all kinds of stuff), and the u-boat cut up to reveal details. We went to a GREAT pub in Birkenhead to watch a Liverpool-Southampton futbol match - very pleasant. As was suggested, I think it makes sense to base in Liverpool, and train to Chester for a day. Easy trip, 45 min. The walk from the station to the historic part of Chester is not long - 1-1.5 km. We were there on Race Day which was a hoot - all the women had amazing collections of twigs and bird remains on their heads.

With the caveat that I visited these spots in late-August/early-September and was limited to places I could reach via public transportation:

• I, too enjoyed the Lost Gardens of Heligan. Both it and the Eden Project are quite large. I can't quite imagine squeezing both into one day. They're rather expensive to rush through the first, only to pay another large admission fee for a truncated visit to the second.

• I'm sure tourist traffic will be much less of an issue during your timeframe, but if a bunch of the restaurants are seasonal, you may have issues, as I did, getting seated for dinner in Cornwall if you haven't made a reservation.

• Wells (smaller) or Bath (many museums) would be a possible stop on the way to Cardiff.

• You'll pass by Ludlow, now a serious foodie town, on the way to Chester. It's quite small, but the half-timbered architecture is worth seeing.

• The sights of North Wales are accessible from Chester.

• You may pass Coventry, with its magnificent modern cathedral, on the way to Bletchley Park.

• Bletchley Park is roughly midway between Oxford and Cambridge, each of which has about a day's worth (or more) or museums to visit.

Here is my detailed review of our 28 day drive tour of Wales and England last year.

Several of your stops are included in my review:
https://www.cruisecritic.com/memberreviews/memberreview.cfm?EntryID=599139

On Day 9 you could stop on your way to Cardiff in Bristol. Visit the SS Great Britain https://www.ssgreatbritain.org/ and take in the Clifton Suspension Bridge. The Clifton area is the posh part of the city with the nicest architecture and places to eat but it's up a steep hill so perhaps drive up!

Day 10 I suggest Castell Coch and St Fagans Welsh folk museum.

Day 12 I suggest departing Cardiff and going to the Roman fort at Caerleon and then on to the Big Pit National Coal museum. You'll then be able to overnight in Hay on Wye (small cute and lots of bookshops) or Hereford (attractive Cathedral).

We can recommend lodging if you give an idea of preference of style and budget.

Also it can be very expensive to take a car across to the Isle of Wight. This trip advisor thread gives could info on catching the passenger ferry. https://www.tripadvisor.co.uk/ShowTopic-g2337531-i31994-k10314331-Local_knowledge_Portsmouth_to_Osbourne_House-East_Cowes_Isle_of_Wight_England.html

Day 7 - you are probably following the A39. A short detour off will take you to CLOVELLY.
When in the Exmoor area, consider visiting TARR STEPS - the kind of bridge that Fred Flintstone would build. It is down some back roads not that far from Wheddon Cross. The village of SELWORTHY - between Minehead & Porlock is also worth a visit - just off A39.
Also visit LYNMOUTH.

Days 10 & 11 CARDIFF:> don’t use city centre hotels due to cost of parking (or no parking). As has been mentioned - see Castell Coch but also throw in Caerphilly Castle. St.Fagans Castle and museum will take at least half a day. In the city centre you have the Museum (good choice if weather is bad) & Cardiff Castle and you would also like to wander around the old arcades as well as the modern malls. Also try and visit Cardiff Bay = 1 mile south of city centre - bus 6 every 10 minutes. (Note that Cardiff Bus don't give change so have plenty of coins).

You might like to consider breaking the journey from Cardiff to Chester by leaving Cardiff on Day 12 and adding a night on the way north? Mention has been made of visiting Caerleon. This is a very awkward place to reach - despite being just N of Newport. I don;t think it is worth it unless you are really into Roman remains. I do think that the suggestion of BIG PIT at BLAENAVON is worth it (free underground coal mine) and this could be added on your way north. So, I would be inclined to do that & then head for Gilwern and Crickhowell and follow A40 NW for a short while before turning R onto A479 and make a stop at TRETOWER COURT. Then continue towards Talgarth (skirting the Black Mountains) before heading to HAY-ON-WYE. You might to consider spending a night in this area (or further on) before heading for Chester. To do this, you will need to head to LEOMINSTER. WEOBLEY is worth a short detour off the A4112. (Trying to go without an overnight between Cardiff & Chester and visit places on the way is pushing it).

Be sure to visit LUDLOW when going up through the Marches (Wales/England border area). Also, just N of Ludlow - STOKESAY CASTLE. Further north, consider visiting https://www.pontcysyllte-aqueduct.co.uk- not far north of Chirk.

Regarding hotels in Cardiff, this comes from my review already posted.
The Sandringham Hotel in Cardiff was located in the city centre. The hotel had no access by car, since the main street of Cardiff, in front of the hotel was marked off as a pedestrian walkway. We parked about 2.5 blocks away in a multistory parking garage and walked to the hotel to check in. The hotel had about 40 rooms starting on the second story of the building. Our room, fortunately, was on that floor. The parking garage just happened to be the one that the hotel had arrangements for discounted parking, so we didn’t have to move the car for two days. We did have to roll and carry our luggage 2.5 blocks to the hotel. Hotel location was perfect, right in the city. The hotel staff was very nice. Breakfast was excellent. The hotel is a small, older hotel and is showing its age, but it was clean, convenient and suited our needs. Also, it was a great value.

Not sure why you decided not to go to Chester, it’s beaitiful and well worth a visit. The Cathedral is fabulous.

I'm still going back and forth between whether to stay in Liverpool or Chester.

Your trip includes 2 areas I have been to in the past 18 months so here are my 2 cents:

• Port Issacs is worth seeing, particularly if you like Doc Martin. We were not fans, but liked the old town.
• Newquay was crowded, hard to park and didn't have anything special so I would skip it
• Consider Tintagel instead of Newquay. It is an old ruin, but has great views of the coast and a lot of history besides Arthur. It has many steps up and down, but worth it.
• Both the Wells and Exeter cathedrals are beautiful and much nicer than the Bath cathedral. The Roman Baths in Bath are worth a visit.
• Driving in Cornwall is a challenge so watch how long you think it will take to get anywhere. Most roads are twisty and very narrow (bushes can brush both sides of the car at the same time) and have 2-way traffic with few places for passing. Having to back up is common. Assume at some point you will have to bend in the side mirrors so there is enough room for the cars to pass. Farm vehicles on main roads is not uncommon. It is hard to make any time when you are constantly worried that the next bend will result in a car headed directly towards you. 10 miles can easily take 20 to 40 minutes or more to drive, particularly if you are trying to find a location like a garden.
• If you are near the Merry Maidens, consider the Telegraph Museum in Porthcurno. Very interesting and still relevant today since many internet cables come ashore for the UK in Porthcurno.
• St Ives is almost impossible to park in. Consider parking in a close town and taking the train. It also has an area where there are driving charges so very hard to drive around.
• As for Glasgow, the Kelvingrove Museum (2-4 hours) and the Peoples Museum (1 hour) are worth visiting. The downtown shopping area if most a pedestrian zone so easy to walk around. The Glasgow subway system works well and avoids having to drive in Glasgow. The main highways cut through the middle of Glasgow so it is complicated to get around Glasgow itself.
• For day trips try Stirling, particularly the castle, which is 30 minutes by train or about 45 by car since it is main highway. Also in that area is Caitness Glass which makes beautiful paperweights. They have a shop and you can see the glass blowing. About 30 minutes by car from Stirling.
• If you like waking, consider the Devil’s Pulpit or other area near Loch Lomond. A drive to Glen Coe would also be possible if you are interested in scenery or walking. Weather would be an issue for these.
  

For Liverpool, you could consider Apple Serviced apartments, very central location.

https://www.sacoapartments.com/serviced-apartments/uk/liverpool/dream-apartments-liverpool/

Hello All Again!
Now that we're home I wanted to send an update on our actual itinerary highlights.

Portsmouth (2 nights)
On the way we stopped at the Fishbourne Roman Palace. Beautiful mosiacs. In Portsmouth we stayed in an AirBnb across the street from the Old Cathedral. It was a wonderful location and we could walk everywhere, We didn't make it to the Isle of Wight as my luggage took a detour to Amsterdam and we ended up having to stay close to the apartment waiting for it. But we did walk around, enjoy the harbor, go to the fort, etc.

Falmouth (4 nights)
We were right on the ocean in another AirBnB and the views were magnificent. We spent one day at the Eden Project and highly recommend it, especially for a rainy day! We did another road trip day to Port Leven (absolutely charming), Mousehole (hard to drive in) and Penzance. And the other day we explored Falmouth, Pendennis Castle, etc. It was too windy for us to brave the ferry to St. Mawes so we missed that.
Wheddon Cross ( 2 nights)
On the way here we visited Port Isaac. Charming fishing village and for us as Doc Martin fans we enjoyed it immensely. At Wheddon Cross we stayed at a marvelous place the Rest and Be Thankful Inn right in the middle of Exmoor National Park. The roads here are very very narrow and windy, the most of anyplace we've visited in the UK. So narrow that we actually punctured a tire getting too close to a wall when meeting a car (which ended up costing 8 1/2 hours waiting for a new one to be delivered.) Beautiful country though. We went to Dunkery Hill area but didn't hike to it due to high winds and rain. We went to Dunster the other day and would recommend that to anyone. Lots to see and do, including a good castle that isn't a ruin.
Chester (3 nights)
We ended up staying in Chester not Liverpool. And we stayed inside the walls in an AirBnB with free parking! The traffic isn't bad at all in November so for anyone considering it don't be afraid of staying right in the walled city. It was very convenient as we could walk everywhere and spent 2 days exploring the city. There is so much to see and walking the walls is a great way to get your bearings and decide where you want to go. The other day we took the suggestion to ferry cross the Mersey to Liverpool. Great way to go. Free parking at the ferry on the Chester side and then we used a Hop On Hop Off bus to see Liverpool. You can catch it right by the Ferry landing so is very easy.
Glasgow (5 nights)
I was nervous that this was going to be too many days in Glasgow but was pleasantly surprised at how much there is to do there! We stayed in an AirBNB in a quiet neighborhood that was a 5 minute bus ride to downtown. Very easy transportation. Highlights here included Clydeside Distillery, Riverside Museum, Kelvingrove Museum, the Cathedral, the Tall Ship, the People's Museum and Winter Gardens (great place for a tea), The GoMa (Glasgow Modern Art Museum), St. Enoch's Square Christmas Market, all the great statues and squares, and much more. Again we used a Hop On/Hop Off for part of the days and just drove down to places with easy parking the others. Another plus to Glasgow is most of the Museums (all that we visited) are free!
Masham (3 nights)
We took our time and visited a couple of sights (what escapes me right now) on the way. Masham is a quiet village (town?) with 2 breweries, lots of great restaurants and pubs, a town market 2 days a week. Plus it is a great location to explore the Yorkshire Dales. We stayed in another AirBnb right behind the main market square and walked everywhere. One day we hit the market day booths, took off on a road trip to Richmond, Barnard, and Middleham Castles plus another town market!
I'm running out of room so will finish in a second post.

Final portion of trip update.
Masham - Another day we toured the Yorkshire Dales and visited Thirsk.
Leighton Buzzard - 2 nights
We stayed here due to it's proximity to Bletchely Park. Bletchely Park is the site of the WWII Codebreakers. It's more than just a museum and includes the Mansion and estate as well as all the WWII huts and buildings. If you are a WWII history buff or if you enjoyed the movie, The Imitation Game, you will find this is an amazing place. We stayed again in an AirBnb, this time right on a canal. We enjoyed watching the canal boats go buy right from our living room.
Last night (airport hotel). On our way we went to Windsor Castle. It was much bigger than I expected and you can spend a few hours here. Currently there are special exhibits and audio about the recent wedding of Harry and Megan, including the magnificent wedding dress and tiara.

And then home for Thanksgiving and snow!
Thanks again for all for the suggestions! We used so many of them!

It appears that you skipped Southern Wales. Too bad, we did Cardiff and found a hotel in the city.
Also, loved Tenby and St. David's.

I understand that you have been to Edinburgh before, so you are going to Glasgow. My research on Glasgow just didn't justify spending time there. We went through there twice on two different cruises on our way to see Edinburgh and places in the east of Scotland.

There are some interesting things to see in Western Scotland. Here are some suggestions:
Loch Lomond & the Trossachs National Park
Argyll Forest Park

I am interested in Roman history, so I would have chosen Chester over Liverpool. We were in Liverpool on a cruise and the main item seems to be Beatles tours, which just didn't interest us.

You have some great sights to see, but you are going to be heading through a lot of traffic, since you will be driving past Manchester and Birmingham (lots of traffic).

You are skipping the Lake District. It deserves a day, even in October. Are you stopping to see Hadrian's Wall?
York is fantastic, I recommend you find a way to visit the city for at least two full days.

Here is our 4 week drive tour of S.Wales and England.

https://www.cruisecritic.com/memberreviews/memberreview.cfm?EntryID=599139

Geovagriffith: While your suggestions may help someone else, note that the OP has come back from their trip. They weren't posting what they wanted to do, they were posting what they already did!

djapapke: I too loved Glasgow on my September 2016 trip, and I agree that for a city its size, there's lots to see and do. I was in Edinburgh in September 2018 trip, and also found lots to do there. They're very different, but both are very worthwhile.