Enter the Unknown is a uncommon Sorcery card from Rivals of Ixalan (RIX), collector number 128. Current market price: $0.34 (foil $1.21), TCGplayer market prices via Scryfall.
Target creature you control explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on the creature, then put the card back or put it into your graveyard.) You may play an additional land this turn.