Recs if you like Underground: A Human History of the Worlds Beneath Our Feet...

Niche nonfiction, aka micro-histories!

microhistory: the intensive historical investigation of a well defined smaller unit of research (such as an event, community, individual or a settlement); it aspires to "ask large questions in small places"

Nonfiction about strange, outlandish, and/or macabre subjects (books that make you more or less go “wtf?!”)