Play Crescent Solitaire at Solitaire Paradise
In the normal game the game is very difficult. The concept is to build 8 foundations from Ace down to King. Only the top card is available to use at any time, so you can only ever move one card at a time. Empty spaces can't be filled!
The other versions of the game are the casual version where you have unlimited shuffles and the easy version which allows you to use the open spaces.