Thundering Falls is a rare Land — Island Mountain card from Murders at Karlov Manor (MKM), collector number 331. Current market price: $18.87 (foil $36.39), TCGplayer market prices via Scryfall.
({T}: Add {U} or {R}.) This land enters tapped. When this land enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)