Over on wikipedia, they have an article about the "Magnificent Seven cemeteries" that tells of a Victorian effort to "alleviate overcrowding in existing parish burial grounds" in London. I'll highlight two of them below but find out more here.
Also on fonc.org.uk, the Friends of Nunhead Cemetery maintain a website with some decent galleries and information on "Perhaps the least known, but most attractive, of the great Victorian Cemeteries of London" here.
Finally, on kensalgreen.co.uk, let it be known that guided tours have started back up as of March 1st and that includes some catacomb tours. Find out more here.