One of my favourite places to visit in London, is Highgate Cemetery. The final resting place of Karl Marx and several other prominent figures.
Although not that old, the western section opened in 1839, is very overgown, atmospheric, and has been described as the victorian valhalla. With all it's gothic tombs and vaults, it's no wonder it's been used as a location for old horror films!
A really beautiful place to visit.
The nearest tube station is Archway, and to visit the western section, you'll need to take a guided tour. Well worth taking the time out to visit though.
Have fun.
