The Sealed Cave, also referred to as the Spawn Area Sinkage, is an anomaly that was added on December 14th, 2015. It is located near the Bridge, behind a cluster of rocks where few billboards once resided on.
It retains the basic properties as the surrounding rocks and cliffs. It is brown in coloration and is textured with the slate material. It is about one stud deep and is not fully visible when viewed afar. It will cast odd shadows around morning and evening and is visible in the road nearest to it.
Back in December 2015, dynamite was tested on the entrance by a team of 3 players. The dynamite had no immediate effect, however, the entrance seemed to shift colors and the lighting of the area shifted.
There were also "leaks" of what seemed to be a cemented entrance to the Sinkage, that opens up to lead to an unfinished part of the tunnel back in 2016. However, after over a year of it is not released to the public, it is speculated that it is a discontinued project.