For example: The player is on top of a mountain over a city, the city and the mountain are both in the open world, but when the player looks at the floor, the game freezes up and lags because it is rendering all that is underneath which is lots of buildings, rocks, and such.

If the player can't see it, why should it be rendered as if he/she can? But the key is I want it controlled, I want the keep the LOD scenery that the player can see but nothing else underneath where he is standing.

You could try an occlusion under the ground.

The game actually has precalculated occlusion and it doesnt render things on the other side of mountains, etc. That may include what the ground blocks already. Regardless, try an occlusion plane, if that doesn't work you may be out of luck.

Sir, you just saved about 30 hours of work. Thanks so much!