Slugterra

Slugterra is a massive underground world existing over 100 miles beneath the surface of Earth-26496. There are 99 caverns in Slugterra, each home to the species native to Slugterra known as a Slug. Every cavern relies on its Slugs to keep it from turning into a dead zone. At the beginning of the series, a battle between Spider-Man and the Jackal causes a hole to Slugterra to be opened, allowing the Shane Gang to get to the surface.