Path of Discovery is a rare Enchantment card from Bloomburrow Commander (BLC), collector number 231. Current market price: $0.20, TCGplayer market prices via Scryfall.
Whenever a creature you control enters, it 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.)