Bunhill Fields, the tiny cemetery just north of the Square Mile, is now a Grade 1 listed park. The burial ground for non-conformists dates back to the 1660s and contains the graves of many famous Londoners.
The City Road cemetery is one of those places that regularly features in articles about 'secret London' (see also Postman's Park and Crossbones Cemetery). It crops up time and again in books by Peter Ackroyd, Iain Sinclair, and their ilk. The non-consecrated ground contains the bones of Daniel Defoe, John Wesley's mum, Eleanor Coade and John Bunyan, as well as a monument to William Blake.
The listed status protects Bunhill Fields from any form of development or interference. 75 of its monuments have simultaneously been granted Grade II listed status.
The Guardian has a more detailed history.
Image by stradders06 in the Londonist Flickr pool.