My wife and I were introduced to an unusual sound chamber a few years ago by a friend in Ouray, Colorado. He took us to the Wiesbaden Spa, a natural hot spring complex at the foot of the San Juan Mountains, and then into the Spa's vapor cave. We sat on benches carved into the sides of the low-ceilinged stone chamber and "toned" in the hot, moist atmosphere for about half an hour at a time (about all one could stand in 100% humidity and 110 degrees farenheit!). The resonance and harmonics as we alternately sang and chanted were rich beyond description. (Unfortunately, it's not a suitable place for most instruments other than the voice.)