personal cave
"We also dig personal caves, which are usually about 1,000 square feet. It's a niche market ?people want caves for all sorts of things, like dining rooms, movie-screening areas, to hold parties down there." - article (via The Trend Junkie)
I always wanted a cave, but I want a real one. It would be cool to have a piece of land with a cave on it. A man made, perfectly round one doesn't seem as much fun but I guess it would do.