Bunhill Fields is - today - a small garden to the north of the City of London, opened on the site of a burial ground used between the sixteenth and nineteenth century. As the ground was never consecrated, it became the favoured burial site for nonconformists, and now is the resting place for John Bunyan, William Blake, Daniel Defoe, several members of the Cromwell family (though not Oliver) and Susanna Wesley (mother of John & Charles), as well as John Benjamin Tolkien, grandfather of J. R. R. of that ilk.
It's often said that Bunhill Fields gives us a taste of what the old burial grounds in London were like before the nineteenth century. Frankly, this is nonsense: Bunhill today is cleaned up, grassed over, with the graves tidily put away behind railings. The coffins, bones and even bodies that nineteenth century writers record as protruding from graves are all gone: all that really remains are some of the gravestones, with epitaphs deteriorated beyond reading.
I also discovered the small Quaker Burial Ground which was once part of Bunhill Fields, but now is hidden away in the midst of a housing development. The founder of the Quaker movement, George Fox, has a tiny memorial beside the wall; the rest of the ground has been turned into a (frankly, not very attractive) garden.
Visiting: Old Street, Moorgate, Barbican and Liverpool Street tubes are all within walking distance. Lots of livings, many dog walkers and some other photographers. Many of the stones are behind fenced enclosures: visit early afternoon in the week or make an appointment if you want to get closer.