October half term - where ?

[exprecis]

We have realised we have enough holiday to both take off October half term but don't really know what to do with it.

Any ideas?

Kids are 8 and 5
We don't want to drive
We aren't big pool/beach people but open to most other things

Things are are considering:

Billund
Efteling
A city break in the UK - maybe Chester?
Crete - to do some sightseeing and some beach
Just staying at home (London) and doing day trips

City break? Rome or Valencia or Barcelona where weather should be clement and there is lots to see and do? Depends on your budget of course.

That sort of thing would be great - sadly we have done all three as city breaks in the last two years!