This clan stayed in their own little town, Annapolis Valley of Nova Scotia, Canada and interbred for about a century. They were discovered in 1984, charged with crimes like sex abuse and child prostitution. 12 members went to jail and the group finally disbanded.
This was every nightmare you could think of, extreme poverty, no access to water or toilets, pedophilia, genetic disorders from the inbreeding and so much more.
This is so utterly bizarre that you need to find out more.