One way Caves are detected is when the barometric pressure changes. The cave will expel or suck in air to equalize the pressure. The bigger the cave the more air moves. If there?s a really big area and the cave is really small between that and the surface the cave will howl and there is a really stiff wind in it.
The caves don?t howl all the time just when wind is blowing through them. But when you have a cave system that howls from time to time you can bet that there is a very large room on the other side.
So how does this apply to plane shift? Sometimes the opening to a very large cave is only 10 cm in diameter. Normally this would be very hard to find. However if it was making a lot of racket one could hear it. Then you get a couple of miners in their to open it up. Another thing if someone was exploring a large cave system and from time to time it howled loudly they would be inclined to look for the very large room that would have to be on the other side.
One of the cool things about this is it would be very easy to implement. It?s also something that really happens.
