Canterbury/Dover Daytrip

Pick either Canterbury or Dover as you won’t have time for both. Taking the train from London will be far quicker than driving. Depending on where in London you are staying will influence which route you use to get to Dover - St Pancras, Victoria or Charing Cross.

Whilst Dover town centre has few redeeming features, the Castle (English Heritage) and the National Trust owned White Cliffs of Dover will fill a day. You may prefer to pick one or the other. It’s a pleasant walk atop the cliffs to South Foreland lighthouse where a guided tour up the lighthouse takes around 40 minutes and there is a cafe. There are underground tunnels at both properties.

I did a day trip to both and found Dover much more interesting than Canterbury-and I usually love churches! Dover Castle is my favorite example of a "real" castle-one built for defense.

I'm going to say the opposite of Cala, we did both in September (not the same day) and much preferred Canterbury over Dover. It's a matter of interest. But I can agree
with everyone else that both in one day is too much.

I too have been researching options for a day trip from London visiting both Dover and Canterbury and I did find this one that looks promising:

Anderson tours, £105/pp, departs at 9am, 10.5hrs, runs on sat/sun/wed. Visits Canterbury (3hrs, cathedral entry incl), Dover castle (2.5hrs, castle entry incl), white cliffs (45min viewpoint).

that tour sounds so rushed!

We took the train to Dover and saw the castle for a couple hours, then took the train to Canterbury and experienced an Evensong at the cathedral. After that, a few ales at a pub and walked around town before heading back to London. We didn’t feel it was too rushed at all. Now, we did not seek out views of the cliffs, so maybe that would have led to the overpacking of sights that some of the other posters touched on. But, IMO, very doable and made for a fun and interesting day trip.

ah but Jay MN you said it all - you took trains there and back. No slow tourbus.

i went to Canterbury with my daughter by train many years ago and but came from Calais on the ferry to Dover. From Dover, we took the bus to Canterbury and spent the night there. We also made a side trip to Leeds Castle (a woman we met in Canterbury offered us a ride there), which we both loved. We did see the White Cliffs when coming into Dover, and I broke out into a rousing chorus of "The White Cliffs of Dover" much to my daughter's annoyance.

As most others have said, I much preferred Canterbury, especially the cathedral.

I'm with Jay, I'd do it. Take an early train from London (maybe around 8:00) get to Dover by 9:30, tour the white cliffs for 2+ hrs, have a quick lunch then tour the castle; train from Dover to Canterbury (takes about 1/2 hr) then visit the cathedral and environs (maybe take in evnsong if possible) have a nice dinner, then train back to London (takes a bit over an hour). Long day but doable and if you're ambitious you can leave London even earlier.

I have been to the White Cliffs numerous times - it’s a 4 hour visit including the lighthouse and tunnels.

On my trip to London, with my then 73 year old father, we took a tour very similar to the one galliegirlie mentions above. Ours stopped in Greenwich, Canterbury cathedral (plus free time, we opted for lunch), Leeds Castle, and the cliffs of Dover (but not the castle). We did not feel rushed at all, and although it was a long day, we saw much more than we would have seen on our own. I think everyone has their own speed that they are comfortable traveling, so whether or not what the OP wants to do is too much is purely subjective.

I have been to the White Cliffs numerous times - it’s a 4 hour visit including the lighthouse and tunnels.

I agree that it's a longer time if you want to hike to the lighthouse and tour it, but not everyone needs to do that, some just want to see the cliffs and maybe do a little exploring around. The tunnels are at, or near, the castle aren't they? Maybe visit the castle, the tunnels, and just get some views of the cliffs and skip the lighthouse. Depends on what you're interested in seeing and how thoroughly.