"The Dictionary of Imaginary Places" by Alberto Manguel and Gianni Guadalupi was one of the best random thrift shop finds I've ever had. It is exactly what it sounds like, an alphabetical listing of worlds from legends and fantasy writings. It covers things like Atlantis, Middle Earth, and even Wonderland.
It gives anywhere from a few paragraphs to a few pages of information describing the world, it's people, and any applicable facts (unique creatures, technology, magic etc.). It even has quite a few maps.
It's 731 pages of great reference material. I highly recommend checking it out if you can.
A quick search and I found it on Amazon for under $20, I'll leave a link if anyone is interested.
https://www.amazon.com/Dictionary-Imaginary-Places-Updated-Expanded/dp/0156008726
you could consider this book from 2000 (you can peek inside on Amz): https://www.amazon.com/Dictionary-Imaginary-Places-Updated-Expanded/dp/0156008726/ref=sr_1_1?ie=UTF8&qid=1484468189&sr=8-1&keywords=imaginary+places