(Vault Cave isn't a spell.)

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

Vault Cave is indestructible. (Destroy effects and lethal damage don't destroy it.)

, Pay 1 life, Sacrifice Vault Cave: Search your library for a Swamp or Mountain card and put it onto the battlefield, then shuffle your library.