The Ruined Abandons have flat floors. In order to enter the temple, however, you will need a slime key (of course) There are many "Shattered" pillars.
Despite the "ancient" look of the Ruined Abandons, it happens to be a great place for growing crops with any chisel dust aside. Any food can be found here; however, Oca Oca and Pogofruit seem to be rare.
- Swap the Abandon in Abandons and the Ruin in Ruined around. Then you'll see why it's called "Ruined Abandons"