I’ve always found esoteric ideas interesting. I put “esoteric” into Google, and the first site that was returned (after dictionary definitions and Wikipedia) was a compilation of Western esoteric texts. It looks interesting.
And if you’d like the definition, here is what Merriam-Webster has to say:
1
a : designed for or understood by the specially initiated alone <a body of esoteric legal doctrine — B. N. Cardozo>
b : requiring or exhibiting knowledge that is restricted to a small group <esoteric terminology>; broadly : difficult to understand <esoteric subjects>
2
a : limited to a small circle <engaging in esoteric pursuits>
b : private, confidential <an esoteric purpose>
3
: of special, rare, or unusual interest <esoteric building materials>
— es·o·ter·i·cal·ly
\-i-k(ə-)lē\ adverb
