From MTG Salvation Wiki
- When a land with hideaway comes into play under your control, you must look at the top four cards of your library and you must remove one of them from the game. If there are fewer than four cards in your library, you look at all of them and remove one from the game.
- The removed card can be looked at by the player who currently controls the hideaway land, as well as by any player who previously controlled that land. The player who controls the activated ability is the player who can play the removed card. It doesn't matter who owns the removed card or who removed it from the game.
- If the land with hideaway leaves play, no one can look at the removed card anymore.
- Each Lorwyn land with hideaway also has an activated ability that allows you to play the removed card if certain conditions are met. This ability refers only to the card removed by the hideaway ability.
- The land's last ability allows you to play the removed card as part of the resolution of that ability. Timing restrictions based on the card's type are ignored (for instance, if it's a creature or sorcery). Other play restrictions are not (such as "Play [this card] only during combat").
- If the removed card is a land, you may play it as a result of the last ability only if it's your turn and you haven't already played a land that turn. This counts as your land play for the turn.
- If you are unable to play the removed card due to these or other restrictions (such as having no legal targets for a spell), nothing happens when the land's activated ability resolves, and the card remains removed from the game face down. You can try to play it later by activating the ability again.
- If you play a card "without paying its mana cost" (as the last ability says), you can't pay any alternative costs (such as those from evoke or morph). On the other hand, if the card has additional costs, you may pay those.
- If you play the land's activated ability and an effect causes you to lose control of the land in response, you can still play the removed card as the ability resolves.
- If the card removed with hideaway has been played or has otherwise left the removed-from-the-game zone, playing the hideaway land's last ability will have no effect.