(Image credit: Gil Klar)

Now you see it, now you don't. This little magic trick is more common with something that's not typically easy to hide: a swimming pool. Still rare but becoming more common, hidden pools come in different varieties: decks (or lawns!) that slide back or fold up, and even floors that drop. A hidden pool costs on average 30% more than a traditional in-ground pool.

The surge in hidden swimming pools | Yahoo! Homes