The Metropolitan Sepulchre was a massive pyramidal necropolis proposed for construction in Primrose Hill in London in the 19th century as a way of addressing the shortage of burial space in the London area. Designed by the architect Thomas Willson, it would have been 90 stories high, and capable of holding up to five million dead.
It was never built, and the need for it was supplanted by the creation of a ring of "garden cemeteries" around London.
References
Metropolitan Sepulchre Wikipedia(Text) CC BY-SA