Abyss

From Syra D&D Wiki

The Abyss is one of the Outer Planes. Its infinite layers are harsh, inhospitable, and impossibly horrific. Acid lakes, toxic clouds, and oceans of magma are just a few of the terrible landscapes contained therein. More terrible, though, are the residents of the Abyss: the demons. Few who venture into the Abyss ever return, and those who do are never the same.