What is this default gray circle

This is zoomed out showing my model which is a large building, and what appears to be a default sort of terrain or horrizon. I can't interact with it. What is it and how do I get rid of it?




This view is a little closer and the scene has a sky box applied


This view is much closer at an angle showing the skybox. You can see the gray circle cutting the skybox off at the horizon.

 

Could be a ton of things. Turn off gizmos and see if that makes it go away. Some of your screens didn't appear, but it may be you are seeing the background because the geometry is being clipped also.