Hogwarts, the Megadungeon

Hogwarts is ancient. The oldest histories known to man cannot say when or how the castle was first built, only that it was founded by four mighty adventurers. Since then it has sometimes lain uninhabited save by the howling of ghosts and the creeping of monsters; at other times it has bustled with life, and successive generations have built additions to it until the original structure is mostly lost amidst the sprawling maze of turrets, courtyards and halls.

Today, only a small fraction of Hogwarts is safe for human habitation. The rest lies in ruins, given over to the lairs of foul creatures and mysterious spirits. And that is to say nothing of the many layers of dungeons and caves beneath the castle, some of which are said to be even older than the building itself. The students, both those of Magic and of Martial Combat, live and work only in the South Wing. They do not have to look far to see the many corridors bricked up, the doors sealed shut with signs that read: Go No Further.

Yet there are some students who are brave or foolhardy enough to disobey the warnings, to slip past the barricades and into the Forbidden Rooms beyond. Indeed, there are those who sit the strenuous entrance exams with no intention of graduating from Hogwarts School of Warcraft and Wizardry - their only goal is to gain access to the castle and make their fortunes by plundering the ruins of their treasure. The school staff deal harshly with anyone found beyond the barriers, but not nearly so harshly as they would be dealt with by many of the horrors that lurk within the castle walls.

The surrounding environs of Hogwarts are not much more secure. The front courtyard and the lawns are generally safe, but the Forbidden Forest is mostly uncharted and there are strange things lurking at the bottom of the lake. The local village of Hogsmeade is where adventurous students go to sell their treasure, which has made it a haven for criminal enterprise. And up on the hill is the Shrieking Shack from which no adventurer has ever returned. All these and more are the dangers - the mysteries - the opportunities waiting for audacious hands to snatch them, deep in the midnight halls of Hogwarts.