Train travel in Wales in August. When to buy tickets

Llandudno to Caernarfon you can actually book as a through ticket if you use station code CFS.

Caernarfon to Cardiff - be careful - the cheapest tickets from Porthmadog are routed via Aberystwyth then the Traws Cyrmu bus to Carmarthen, then the train to Cardiff. That route is like crazy cheap. So if you want to do train all the way be careful to check it is routed via Shrewsbury and doesn't look too cheap to be true. I encourage the bus route but it is a long journey.

Manchester Airport to Llandudno is £45.40 on the day before railcard discounts, but only £8.50 Advance Fares (at 10pm tonight for tomorrow morning). I wonder if it is worth buying an Advance for a train say 90 minutes after landing, another one for an hour later, and another one for an hour after that.

Cardiff to LHR will obviously be cheaper now, but there will be advance tickets closer to the time, or use the frequent direct National Express bus.

Bangor to Cardiff can be done by direct train in 4 hours 19 minutes. Paying today to travel today would cost about £54 each but pre booking a few weeks in Advance for specific trains >(no refund) would cost about £40 each (with Railcard - will be less). However, going this way means that you retrace your route as far as Chester. That being so, you may wish to take a bus from Caernarfon to Porthmadog and then use a train on the Cambrian line which goes down the coast as far as Aberdovey (Aberdyfi in Welsh) where the route then turns inland to cross mid Wales to Shrewsbury - where you change trains for onward that will take you to Cardiff. Going this way takes 5 hours 46 minutes from Porthmadog to Cardiff.
https://www.visitwales.com/destinations/north-wales/explore-cambrian-coast-railway-line

You can check the train prices and times/book on the following site even though you will not be travelling with Scotrail. By all means compare for clarity with other sites as well. Play around with dates to see how the fares vary over time. https://www.buytickets.scotrail.co.uk

Another way you could do the journey is Traws Cymru buses - and I do mean buses rather than luxury coaches!

Map of rail routes in Wales (grey = Traws Wales bus routes).

Don't forget to retain your tickets to get 2 for 1 entry into CADW Castles such as Conwy & Caernarfon.
https://tfw.wales/ways-to-travel/rail/savings-and-offers/cadw

Thanks everyone! One advantage to the Caernarfon to Porthmadog to Cardiff route is it will be new territory for us, so that might be worth the extra hour and a half on the train. Is it a more or less scenic route than going Caernarfon to Bangor to Chester to Cardiff?

Yes - the Cambrian Line is more scenic than the north Wales Coast Line - which is nothing special on the first leg out of Chester. Chester by the way, is well worth a stop if you can fit it in - though if you have Advance tickets - you would have to split them at Chester. You can see a British TV programme about the Cambrian Line here - though it does skip some things that I think should have been mentioned. https://visitcheshire.com/locations/chester

Note that when you reach Porthmadog that the Cambrian Line station is at the north end of the main street and should not be confused with the narrow gauge steam railways found at the south end of town.

The trains used on the Cambrian Line are known to have unreliable air con. A coach with closed windows indicates that the air con is working. New trains may be on this line by the time you arrive as they are currently making test runs.

You may also like to know that a narrow gauge steam railway links Caernarfon with Porthmadog though not sure that you would want to use that plus the long trip down to Cardiff all on the same day. https://www.festrail.co.uk

PS. When in Llandudno, you may wish to consider visiting Bodnant Gardens by using Bus 25. You can find the schedule here & select all the stops & the day of travel.

You can also use the same site -https://bustimes.org - to find other local buses - such as the 32 from Cardiff to the Museum of Welsh History at St.Fagans Castle - about 7 miles west of the city centre. (No bus on Sundays and note the last one back is about 3pm so best to go out on the first bus).

Also note that whilst in Cardiff, you may wish to visit the medieval castle at Caerphilly - about 8 miles N of the city. Buy return train tickets on the day and on arrival at Caerphilly Castle - show the tickets to get 2for1 entry.