The Grotto is an expansion to the ranch set inside a (slightly spooky) cave that allows a rancher to care for light-sensitive slimes without the need for a solar screen. Never has a phosphor slime felt so liberated. - Slimepedia
Dark and wet, perfect for phosphors. In the center of the Grotto, (which looks like a large cave, with stalactites) there is a huge gaping hole covered with wood planks (just like the bridges) and you can see a pool of water at the bottom. Once the "Grotto Upgrade" perk has been obtained at 7Zee Rewards Level 12 (Playful Fox II) crystals not unlike those in the glass desert will appear on the ceiling, and the gates and paths will be affected by previous 7Zee Rewards Club perks.
If you go through one of the tunnels of The Grotto, you'll get to a cliff. Behind the teleporter situated in that cliff you'll see the Spring Archipelago. This row of islands leads you to Feral Canyon, being that the archipelago's main function. The jetpack is required to navigate through islands.
- Because the Grotto is confined, you can use it as a much more free place to ranch slimes.