In the DC Universe, the Hollow Earth is know as Skartaris, and September 24, 2005 it got the full animated treatment on an episode of Justice League Unlimited: Chaos at the Earth's Core.
episode synopsis:
"Supergirl, Stargirl, S.T.R.I.P.E., and Green Lantern help Warlord liberate Skartaris (a hidden world inside the Earth's core) from Deimos, a brutal dictator while protecting a very large piece of Kryptonite from Metallo and Silver Banshee. Originally titled "Heart of Stone"."
