Art historians consider it one of the most prestigious collections on Earth, but alas, you cannot visit this year. It’s undergoing a £50-million renovation until 2020. Somerset House (www.somersethouse.org.uk), its home, was once a naval complex and later was where Londoners came to settle taxes. Now it’s a favorite hangout. The courtyard, beneath which lie the foundations of a Tudor palace, has a grove of 55 ground-level fountains that delight small children, and it’s the scene of both popular summer concerts and a winter ice rink. Free 30-min. tours go Tuesday, Thursday, and Saturday from the information desk in the Seamen’s Hall; check ahead for timings since they may change if something else big is going on. Also look for changing exhibitions (either free or £10 adults, £8 seniors/students depending on what's on). The Victoria Embankment terrace overlooking the Thames (from across the street) can be enjoyed for free.