Amsterdam's Bibliotheca Philosophica Hermetica (AKA "The Ritman Library) houses more ths 25,000 occult texts, covering "Hermetics, Rosicrucians, Theosophy, alchemy, mysticism, Gnosis and Western Esotericism, Sufism, Kabbalah, Anthroposophy, Catharism, Freemasonry, Manichaeism, Judaica, the Grail, Esotericism, and comparative religion."
The library has begun to scan and post its core collection to an online archive called The Hermetically Open Archive. The project was underwritten by Dan Brown in thanks for the library's contributions to his books "The Lost Symbol" and "Inferno" (the library houses the first illustrated edition of Dante's "Divine Comedy," from 1472).
Haute Macabre has assembled a kind of highlight reel of the collection, which has some gorgeous illustrated texts in it.
Hermetically Open [Ritman Library]
Bury Us Beneath Occult Books: The Ritman Library Digitized [Maika/Haute Macabre]