Splitting Five days between Canterbury and where?

That’s a long time for that town. You could go visit Dover castle and the WWII tunnels or visit Leeds castle.

Dover Castle is worth seeing, not far away. Will you have a car or rely on trains/busses?

Thanks for asking. We will not have a car.

We actually are thinking of splitting the time with another location, so if there are suggestions please say them. We will have been to Bath, Windsor, Salisbury, Wells and York and will head for London after as I said.

Take the ferry across the channel to Calais? Not sure what you’re going to do in Canterbury for 5 days.

• I highly recommend the docent's tour of the cathedral, it's about £5 extra. There's also a small museum in the crypt that is well worth the time.
• We enjoyed the Roman Museum. It's small and will only take an hour.
• Canterbury is extremely walkable and well worth just wandering. We walked outside of the West Gate and found a great Mexican restaurant called Cafe Des Amis.
• Everybody but me seems to have liked Dover. It's a short train ride away.
• If you had a car I'd highly recommend a daytrip to Bodiam Castle and nearby is the Battle of Hastings site. We loved both and consider them must-see. I don't believe it's doable though without a car.

Take the ferry across the channel to Calais?

As on a number of other posts taking the foot ferry to Calais is now very difficult, as very few sailings now offer that service, and Calais port is now well out of town.

Ramsgate (by train or bus) is a good day out- lots to see and do there- I think I have written a post on that, and Pegswell Bay is instrumental in why Canterbury as a city even exists. This is a good chance to learn more about English and 'Viking' history. I put Viking in quotes because there is an academic difference of opinion as to whether the landings at Pegswell Bay were by Vikings or by invited Danes who then became pseudo Vikings, about 3 centuries before what are widely regarded as the first Viking raids on the UK.
We are not going to resolve that debate here on the forum.

Chatham Historic Dockyard is another great day out from Canterbury.

Leeds Castle is an easy day out by transit, as is Royal Tunbridge Wells.

Linking back to Pegswell Bay there is also a lot of good walking thereabouts, old pilgrimage routes to Canterbury, including the Augustine Camino from Ramsgate to Canterbury.

a daytrip to Bodiam Castle and nearby is the Battle of Hastings site. We loved both and consider them must-see. I don't believe it's doable though without a car.

Bodiam Castle is not hard to do by transit- Train Canterbury West to Headcorn then bus #12 to Tenterden then the Kent and East Sussex steam railway-
Other routes to Tenterden also exist- that is the easiest.

For Battle go to the eponymous station- either via Ashford, the Cinque port of Rye and Hastings (two worthwhile stop offs) or via Tonbridge- both from Canterbury West.

You could even do that as a round trip- out one route, back the other.

Talking about Cinque ports Walmer Castle (an extension of your trip to Dover) is another worthwhile visit (Dover is another of the Cinque ports- a bit of it's history that everyone misses).

Hmmmm, the P&O Ferry site seems differ on your opinion. I only offered it because a Rick Steves guide once suggested it to us as a day trip for that area.

https://www.poferries.com/en/routes/dover-to-calais/travel-information/travelling-as-a-foot-passenger

I like Margate. It's maybe a bit low brow for the more cultured travellers among us on here, but it's nice, slightly faded Victorian seaside resort. Walking along the seafront from Margate to Cliftonville is pleasant. The Turner Contemporary Gallery is an attraction if you like modern art. Current and upcoming exhibitions include Mark Leckey, who I'm a big fan of, and Anthony Gormley, one of the UK's most important contemporary sculptors. Quite a few of the London arty crowd moved down there some years ago, including a friend of mine and his family, who love it.

Hmmmm, the P&O Ferry site seems differ on your opinion. I only offered it because a Rick Steves guide once suggested it to us as a day trip for that area.

I don't doubt that but things change. Once all sailings by all companies did foot pax 24 hours a day. That got reduced to not from 2200-0600 then to P and O only, then to, as I said very few sailings a day- 6 a day each way counts as very few.

Bear in mind that you now check in 90 minutes (previously a far shorter time) before departure and are now last off ship 30 minutes after arrival, and the port has moved twice- things have changed markedly since the RS guide correctly and reasonably suggested it.

So the first foot pax sailing is at 1005- latest check in 0835 (so early start from Canterbury at 0640), allow the time change, that is 1300 off the ship, arrive in the town centre say 1330.

The last foot pax sailing at 1900 (check in by 1730) is late for getting back to Canterbury (at 2146 at best, maybe 1 hour later), as it'll be 2000 or later when you leave the ship.

So the previous 1720 sailing is check in by 1550- say 1515 from the centre of town.
You have had under 2 hours there for all that effort- back at Canterbury at 2046 (or 1946 if very very lucky). Even the 1900 return scrapes you 4 hours in Calais.

The killer is the long check in time as is the hanging round on arrival waiting for the bus from the car deck to the terminal building.

Also the bus P and O talk about is reported by recent actual travellers to be not super reliable.

Hoiw about somewhere like Rye ? It is a lovely old fashioned place with narrow cobbled streets and a lot of character. It has an interesting history and also had strong links with smuggling. Stop in the C15th Mermaid Inn

We are going to be in Canterbury next May and are planning daytrips to Dover and Whistable. You can rent bikes to ride to Whistable or there is a bus that runs regularly. It is a sea side town that I thought looked interesting, although I obviously haven't been there yet. Perhaps others can comment who have.

The Whitstable cycle way is 7 miles long, using an old railway route and is known as The Crab and Winkle Way- as was the old railway affectionately- https://explorekent.org/activities/crab-and-winkle-way-canterbury-to-whitstable/

Whitstable is best known for its oysters (and seafood generally, hence the Crab and Winkle name).

It is a very nice town full of historic buildings, although usually very busy with tourists.