Potion-Mixing Room

   This, unsurprisingly, is a room with very thick walls, custom carved out of the rocks to be the place where the ka-boom would literally have to be earth-shattering to be a real problem. However, we can combine the functional with the aesthetic, and generation upon generation of Hogwarts students have added to the decor here, until you'd never know you were underground.

Draco's deliberations
Mr. Malfoy came in here a few times, and wrote his detestation of his rival on the walls.