The Infernal Plains are a group of volcanoes and lava fields which are located in the middle of Thanatos. They are filled with deadly perils, and only the toughest lifeforms can survive here.
The Infernal Plains are basically gigantic lava fields, filled with many volcanoes and calderas. They extend for miles, and the entire area is very hot, with a temperature of 180-200 degrees F. However, that is only during the day. At night, this drops to a freezing -30 degrees F.
But regardless of the time of the day, the lava fields are active, and many new rivers of lava form every hour. The only source of liquid water is in boiling lakes, and these have so much sulphur that they are undrinkable. Incredibly, a few lifeforms are able to survive in here. The rest of the water is poisonous vapor, which often erupts from huge geysers. A few lifeforms have adapted to 'drink' the poison, however.
Massive amounts of CO2 erupt from the lakes and volcanoes, making the air unbreathable to most forms of life.
Incredibly, life exists here. The vast majority is either underground or nocturnal.