I did about 10 walking from where I was staying to the British Museum then the Natural History Museum in London a couple of years ago (plus however long I was walking about in each) and thought my feet were going to fall off but that's likely because I am a blimp.

I'd planned to walk all the way back as well but got about as far as the pub where the Great Train Robbery was planned, thought "fuck this", had a couple of pints and did the rest of it by tube.