This lake is a large crater occupying most of Jungle Island. It is surrounded by cliffs and overlooked by the Rivenese village. There is an underwater railway which serves a submarine train, reaching several stations around the Lake, each of which has a retractable ladder. At the center of a lake is a rotating periscope, which Gehn controls from his observatory on the Survey Island and uses to spy around the Lake.
There must be at least one living Wahrk in the lake.
The stations around the Lake are:
- Village dock
- The starting point of the submarine. This station is also an elevator that brings the submarine down or up to a vantage point with thrones and hearths (obviously for Rivenese officials).
- A schoolroom for Rivenese children. Here there are plaques with the D'ni alphabet, the three "Rules of Gehn" in the D'ni language on the chalkboard, and a gallows toy for teaching the D'ni Numerals. There is also an Imager with a recorded message from Gehn to the students, chanting some D'ni hymn.
- Control Tower
- Here there are switches that control the position of the ladders (up/down) on all stations around the lake. A window provides a view over the lake.
- A structure that reaches from the lake surface to the level above, connected with the prison. It is overlooked by a tower whence Gehn can control the gallows mechanism and open the platform to feed the prisoners to the Wahrk. The gallows also serves as an elevator to the above level. Sometimes, when on the gallows, one can hear the Wahrk bumping against the structure.
- This position lands on a wooden platform near the Lake surface.