Gate to the Aether is a rare Artifact card from Mirrodin (MRD), collector number 174. Current market price: $2.82 (foil $16.50), TCGplayer market prices via Scryfall.
At the beginning of each player's upkeep, that player reveals the top card of their library. If it's an artifact, creature, enchantment, or land card, the player may put it onto the battlefield.