Explorer's Scope is a common Artifact — Equipment card from Zendikar (ZEN), collector number 202. Current market price: $0.24 (foil $2.69), TCGplayer market prices via Scryfall.
Whenever equipped creature attacks, look at the top card of your library. If it's a land card, you may put it onto the battlefield tapped. Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)