If you buy admission to St. Paul's Cathedral you can go back any time for a full year, and it took me two trips to see everything and really do it justice. The free guided tour was absolutely wonderful – my guide spent 3 hours taking us round, when it should have been 2 hours but was extremely informative. The huge number of steps up to (nearly) the top of he dome can be done in stages, stopping off to view the Whispering Gallery, and there is seating at that level too, and although the climb is hard work, the views from all around the top are spectacular. Going in October as I did, meant I didn't have to queue to go round the top level, but I understand it gets very busy in the summer months. The crypt is also spectacular.
