At the Goonhilly Earth Station visitor centre (currently closed), there are two sound mirrors set up at opposite ends of the centre indoors, allowing people to communicate across the whole room. The effect is really quite weird.
Many galleries in domes have the same property - if you ever go to a large concave concrete dam, you can use a similar phenomenon to talk to someone on the far side.
There's also an example in Techniquest, Cardiff (UK) www.techniquest.org.