Located in South Kensington, this beautiful Victorian building houses some of the most weird and wonderful items from the natural world. You can see the dinosaur bone collection, visit the creepy crawly room, learn about the mammals from around the world and come face to face life-sized blue whales, elephants and elk. Each year they have an incredible Wildlife Photographer of the Year exhibition (£10 entry).
If you want to avoid the queues (and screaming children) the museum is open on the last Friday of every month until 10pm, complete with live music and a bar! http://www.nhm.ac.uk/