slugs, and the setting of the show,Slugterra. The underground world of Slugterra. SlugTerra is a massive place, divided into 99 caverns, each with their own slugs and history. In episode 1 of Slugterra it says there's only one way back to the surface. Some believe it's through the 99 caverns and the Slug's energy. Acording to Eli there are great evils hidden beneath Slugterra held in check by the energy of the slug.