Hideaway it triggered ability that is paired to an activated ability of the same card. The ability has only appeared on five land cards from Lorwyn, but these few cards have seen plenty of tournament play.

When a land with hideaway enters the battlefield, the hideaway ability will trigger. When this trigger resolves, the controller of the hideaway land will look at the top four cards of his or her library, choose one, exile it face down and put the remaining three cards on the bottom of their library in any order. The face down card can be viewed by anyone that has controlled the hideaway land at any point after the hideaway ability has resolved.

Hideaway lands all have an activated ability that allows the controller of the land to play the card that was exiled by the triggered ability. Technically speaking, these activated abilities can be played at anytime, but the exiled card can’t be played unless some other condition is met. For example, Windbrisk Heights‘ ability that allows you to play the exiled card requires that you have attacked with three or more creatures that turn. As this activated ability resolves and assuming the condition is met, the controller of this activated ability may cast the exiled card.

If the exiled card was a land, it cannot be played unless it is during its controller turn and they have not played a land yet. If this card is a spell, it will use the stack like other spells and can be countered.