The face-down variation, or face-down version, of Pyramids - Tripeaks Solitaire game is pretty much the same as the face-up variation, whose rules can be read following this link.
The only difference is that those cards on the pyramids with parts of other cards above are face down, that is, covered. For example, when the game starts only the cards in the lower row are face up, as you can see in the next image:
As the player removes cards from the pyramids, those cards that remain on the pyramids without any part of other cards above become face up, that is, discovered.
Therefore, as the player has less information, luck has more to do in this version of the game.
Learn how to play in ludado by reading the rules about how to play the face-up version of the game, rules that can be read following this link.
It can also be interesting to read these posts: 'Pyramids: Mastering the game (I)' and 'Pyramids: Mastering the game (II)'.
I want to play
You can play online here.