“Whoever left the facility also left the majority of their work behind and intact. No theorems or tomes, unless they’ve been removed—and I doubt Teacher removed them—but, as I’ve discovered, it’s possible to trigger … tests. Theorem models that they would have used. Most of the chambers down there were used to prepare for something, and they were left in a state where anyone who comes across it can re-enact the setup. Someone left—challenges—down there for any necromancer talented enough to understand what they were doing.”
“Stop being opaque, Nonagesimus. What do you mean by challenges?”
“I mean,” said Harrowhark, “that I have lost one hundred and sixty-three skeletons to a single laboratory construct.”
“What.”
“I’m prevented from seeing whatever destroys the skeletons I raise,” came the terse answer.

Gideon the Ninth - Act Two, Chapter Thirteen