Moat

The moat is the body of water surrounding HQ. It is referenced in the title "Master of the Moat." It is the home of Octobella and Percival, as seen in "Gekko Everywhere," or, more specifically, a Crystal Garden, as seen in "Octobella." Also in the moat is an Underwater Cave.
In Season 1, the moat's depiction is slightly different, lacking the entrance to the Underwater Cave, and is an empty sea surface inhabited by sea creatures.