Layover; children at home; business constraints. Whatever the reason. If I only had two full days in London here is what I would see.
Churches
St. Paul’s Cathedral and Westminster Abbey are musts. For something more discrete I suggest the Chapel on the grounds of the Tower of London.
Museums
So many to choose! I would start with the Churchill’s War Rooms and the National Gallery. The latter is free. Additionally, London is filled with wonderful museums that, while amazing, are not going to attract the same crowds as the National Gallery. I recommend Apsley House which showcases an impressive collection of gifts from a grateful Europe to the first Duke of Wellington following his victory over Napoleon. Next, the Wallace Collection in Manchester Square has one of the most important collections of French furniture and art in Europe. J. Paul Getty who lived just outside London and knew a bit about art was a frequent visitor.
Strolls
Each area of London has its own unique charms. Just to highlight a few; Bloomsbury is home to the University of London and British Museum. St. James includes Pall Mall, Green Park, Horse Guards Parade and, of course, the Ritz Hotel. Mayfair radiates from Grosvenor Square and includes the most expensive real estate in London.
Dining
For the classic English dining experience, I recommend Rules restaurant founded in 1798. It was “M”’s favorite hangout in one of the more recent James Bond movies. The story is that the producers hired out the entire restaurant for 3 days for a 50 second scene in the movie.
For another special dining experience, I recommend the Royal Automobile Club in Pall Mall. You need to be a member or reciprocal member but it’s well worth the effort.