tissington Trail - Ashbourne, Derbyshire
High Peak Trail - Cromford??, Derbyshire
more details here
You could camp on the outskirts of London and cycle in to places like the Imperial War Museum (its free too)
Pembroke was mentioned
- don't forget the castle.
Stratford Upon Avon, lots of good cycling around there and history
Dare I say, Birmingham has become a mecca for tourists


What are the kids into?