Underdungeon - The Ambaret Wing
In the eastern reaches of the Lower Dungeons of Castle Hogwarts, there is a tunnel, which appears to be a sewer pipe of some sort – a low, dark, arched hallway at the base of the stairs. About a hundred meters in, on the left hand side, if you tap the wall with your wand, your wand will not tap, and instead sink into the wall, as though sinking into a moist sponge.
“Magic is a Treasure to be carefully guarded.” That is what the curious must recite to pass the wards erected by the Four Traditional Founders of the Hogwarts School for Witchcraft and Wizardry. The rock wall falls away, like candle wax, leaving a pile of pebbles at the seeker’s feet.