Slugterra is a massive underground world, 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. According to Eli there are great evils hidden beneath Slugterra held in check by the energy of the Slugs.
Far and above, SlugTerra is largely populated with Humans and Slugs. However, it is also home to a number of other species, both humanoid and otherwise. While some species, such as Slug Hounds and Molenoids have a clear terran counterpart, other creatues such as Behemoths seem to be fully unique to this underground world.
- SlugSlinger: Being a slinger is a full-time job! It's an action-packed career choice, full of travel and adventure. Almost all residents of SlugTerra have at least a small amount of slinging skill, but a handful have dedicated their lives to slinging.
- Security Slinger: Often disparagingly referred to as "mall cops", the Security Slingers are a close-knit group who uphold justice in malls across SlugTerra. They're surprisingly skilled slingers and take their jobs very seriously.
- Prison Guard: Guard prisons, such as Stalagmite 17.
- Entertainment Slinger: The best of the slingers can make a career out of showing off their skills with a blaster. Mario Bravado is a beloved trick-shot slinger who stars in his own show.
- Slingersmith: Blastersmiths design, build, and repair blasters. As with any crafts-person, there are different levels of skill within this field. Red Hook is a master Blastersmith, considered by many to be the best in his field.
- Miner: Miners work at mining caverns, usually mining gold or Dark Water, in case of Blakk's workers. But being a miner in SlugTerra isn't as easy as it seems. Some mining caverns contain Dark Water, and miners often get assaulted by Blakk, who makes them leave the cavern to continue with his ambition.
List of Caverns
- Main article: The 99 Caverns - This is a list of only a few of the known caverns in SlugTerra, so to see the full list please visit the main article.
- Chillbore Cavern (home of the Frostcrawler Slug)
- The Crystal Cavern (home of the Geoshard and Crystalyd Slugs)
- Deadweed Cavern (home of the Frightgeist Slug)
- Forgesmelter Chamber (home of the Forgesmelter Slug)
- The Jungle Cavern (home of the Boon Doc, Enigmo, Vinedrill and Hoverbug Slugs)
- Land's End Cavern (home of the Rammstone Slug)
- Quartermain Cavern (home of the Earth Elemental)
- Quiet Lawn Cavern (home of the Grenuke, Hop Rock and Phosphoro Slugs and the Energy Elemental)
- Snowdance Cavern (home of the Slyren Slug)
- Tusker Forks Cavern (home of the Tazerling Slug)
- Undertow Cavern (home of most Water Slugs and the Water Elemental)
- Upright Cavern (home of the Fire Elemental)
- Wild Spores Cavern (home of the Flatulorhinkus Slug)
- Wind Farm Cavern (home of the Hoverbug and Tormato Slugs and possibly the Air Elemental)
- Main article: The 99 Caverns
- Cavern Sea Reef (located beneath Undertow Cavern's seas, this is the home of water dwelling slugs like the Aquabeek)
- The Deep Caverns (technically not apart of SlugTerra but still part of the underground - This is the home of the Darkbane)
- The Eastern Caverns (also technically not apart of SlugTerra but still part of the underground - This is the home of Junjie and his Infurnus, Joo-Joo, and now it's also the temporary home of the Shane Gang)
- Cinder Rapids (home of the ultra rare Infurnus Slug and possibly Flaringoes)