The Chamber of Echoes is a cross-shaped room. The floor of the central square sloeps down to a level five feet lower than the rest of the chamber. The ceiling above this central square forms a shallow dome, its height reaching almost thirty-five feet above the lowest area in the chamber. The ceiling of each of the 'arms' of the cross slope upward from a height of ten feet at the outermost edge to twenty feet high around the central square. The walls, floor, and ceiling of the chamber are all curved from solid stone. They are smooth but not polished.
The construction and geometry of the room is such that it has the following properties:
- All sounds in the room are amplified into the central square. This effect is so pronounced that a quietly whispered word spoken at one of the doors can be clearly heard by someone standing in the room's center, although that same word would not be audible to someone standing at another door.
- Characters walking anywhere in the central square will hear footsteps and may pause to peer about in confusion trying to determine who it is they are hearing. They may even fear that there are invisible assailants about. In fact, the footsteps that they hear are their own. Any sounds generated in the central square will be amplified and focused back into the chamber's center.
- A loud noise, such as a shout or metal striking metal, made in the central square is almost deafening to any creatures located there. Very loud noises, such as a large creature's roar or a magically created sound, can be dangerous and will do actual physical harm.
If the DM desires it, perhaps the amplifying properties of the room apply not only to acoustic energy but also to arcane energy. The possibilities are interesting...
I would recommend that this chamber be placed somewhere in your megadungeon that is fairly commonly travelled. Perhaps it is on a well known route from one major area to another. It would serve as an interesting traffic sorting device. Once the characters have become familiar with it and its effects, you can then change conditions such that its effect on arcane energies becomes apparent. Now the entire nature of the chamber and its role within the megadungeon changes.