Just for fun, OTO = Ordo Templi Orientis. Heavy into Egyptian and Masonic symbolism, plus the usual Crowley stuff.
Symmonds "The Great Beast" is a good read. And if you want to see how the Golden Dawners, Crowley types think, Israel Regardie's "The Eye in the Triangle" is kind of fun, with some neat pictures. He was Crowley's secretary for a while.
As Magister Svengali stated below, from the historical and curiosity perspective, it is interesting to read.
"Consensus is the absence of leadership." Margaret Thatcher
"I'm fascinated with how primitive the human mind still is. It can be misdirected so easily." John Gaughan
"Success is uncommon. Therefore, not to be enjoyed by the common man." Cal Stoll