Skartaris was a mysterious land deep in the Earth's under the Arctic.
Powered by a small red sun, the world of Skartaris was home to many different tribes and nations, and had a diverse wildlife that included dinosaur species that were extinct on the outside World. Several people were able to travel from the outside to the inside via a hole in the North Pole.
Skartaris was created for First Issue Special #8, Warlord's comics debut. In this world view, the Earth is hollow; the core is in fact a small red sun. Skartaris lies on the inside of the sphere, creating a unique sky on which the lands on the other side could be seen. "Chaos at the Earth's Core" is more consistent in this than the comics; on more than a few occasions artists would give Skartaris a generic blue sky.
In the DCAU, the Earth is not hollow. According to Dwayne McDuffie, Skartaris is located in a pocket dimension.