Explorer's Scope is a uncommon Artifact — Equipment card from Conspiracy (CNS), collector number 198. Current market price: $0.17 (foil $1.09), 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.)