Lake R'lyeh

Lake R'lyeh is a large lake located on Monster Island and is Cthulhu's home. It was originally his place of slumber, but is now where he takes residence when the cephalopod is not being a nuisance.

Pre-ProjectGodzilla
Lake R'lyeh was a large body of water on the part of the continent of Mu of the planet Earth that would later become Monster Island. When Mu sunk into the ocean, Cthulhu took residence in the lake and fell into a deep slumber in the depths of said lake.

Episode 4
Upon arriving at Lake R'lyeh, General Grievous and his gang attempt to summon Cthulhu with the help of their latest recruit, Mesogog. After tossing their sacrifice in the water, they proceed to summon the Dark One, only to have Lord Zedd mess up the ritual phrase and summon King Ghidorah by accident. Eventually, they summon Cthulhu, but the chaotic deity eats Mesogog and escapes before Grievous can say or do anything.

ProjectGodzilla X
To be added.

Behind the Scenes
The body of water used for Lake R'lyeh in ProjectGodzillaβ was actually a water hazard pond for a golf course at a former apartment complex Joe used to live at. Originally, when they first filmed Episode 4, they were going to use a kitchen sink, with Grievous breaking the fourth wall and claiming that "they cannot afford to film on location" when called out on said sink not being the ocean (despite the fact that at the time, Joe and Keizer lived roughly 10 minutes from the nearest oceanfront beach).

Trivia

 * Lake R'lyeh is named after the fictional lost city of R'lyeh from the H.P. Lovecraft story Call of Cthulhu.