Scholomance

"As I am on the subject of thunderstorms, I may as well here mention the Scholomance, or school supposed to exist somewhere in the heart of the mountains, and where all the secrets of nature, the language of animals, and all imaginable magic spells and charms are taught by the devil in person. Only ten scholars are admitted at a time, and when the course of learning has expired and nine of them are released to return to their homes, the tenth scholar is detained by the devil as payment, and mounted upon an Ismeju (dragon) he becomes henceforward the devil's aide-de-camp, and assists him in 'making the weather,' that is to say, preparing the thunderbolts."

--Emily Gerard, "Transylvianian Superstitions" (1885)

It is said this magical school was founded by the Solomanari, originally Zgriminties or Hultan, shamanic priests worshipping the deity Zalmoxis. They claimed power over storms, and it was said they can someone a dragon-like creature or wyvern as a mount. Likely, it started as a temple for the worship of Zalmoxis, the Un-Dying God, who was said to have died, descended into Hades, and returned. Zalmoxis' home was a cave beneath a sacred mountain. His priests were described by the Romans as dwelling beneath the earth as well, in "underground chapels." The Scholomance was also underground, apparently on the mountain, but with tunnels extending beneath a nearby lake.

"They believe they are immortal in the following sense: they think they do not die and that the one who dies joins Zalmoxis, a divine being; some call this same divine being Gebeleizis. Every four years, they send a messenger chosen by chance to Zalmoxis. The mission is performed in the following way: men standing there for that purpose hold three spears; other people take the one who is sent to Zalmoxis by his hands and feet and fling him in the air onto the spears. If he dies impaled, they think that the divinity is going to help them."

— Herodotus, Histories 4:93

The most famous student of the Scholomance was Dracula himself. According to Stoker, members of his family "had dealings with the Evil One. They learned his secrets in the Scholomance, amongst the mountains over Lake Hermanstadt, where the devil claims the tenth scholar as his due.” It is unclear which of the glacial lakes near the town once-called Hermanstadt (now the idyllic Sibiu) Stoker is referring to, but its likely Iezerul Mare (“Lake of Howls”), the largest.

"Here we find that the drac is the devil in person, who instructs certain persons to be magicians and medicine men in a college under the earth. Of these, one in eight receives instruction during fourteen years, and on his return to earth he has the following power. By means of certain magical formulae he compels a dragon to ascend from the depths of a loch. He then throws a golden bridle with which he has been provided over his head, and rides aloft among the clouds, which he causes to freeze and thereby produces hail."

--R. C. Maclagan, in a report for the journal Folklore (1897)