Ruins
From DominionStrategy Wiki
Ruins are non-kingdom cards which are only included in games with at least one Looter. The number of ruins used in any game is equal to the number of Curse cards. Specifically, 10 ruins for each player after the first. There are 5 different ruins cards, with 10 copies of each card. When setting up the ruins piles, shuffle all 50 ruins cards together and then randomly select only however many are needed for the game. Only the top ruin is visible at any time.
The different ruins cards are: Abandoned Mine Ruined Library Ruined Market Ruined Village Survivors