(Centaur Cavern isn't a spell.)

At the beginning of your end step, if you didn't cast any spells this turn, Centaur Cavern deals 1 damage to you.

All creatures have Swampwalk.

, Pay 1 life, Sacrifice Centaur Cavern: Search your library for a Swamp or Forest card and put it onto the battlefield, then shuffle your library.