This was the previous flank to the right side of the pit in MVM Underground. I thought it was too visually distracting, especially when first entering the map from spawn.
This is the new side of the pit, which keeps the area around the pit more symmetrical and conducive to vertical combat.
You can see in an overview of the pit area that the flanking bots now get visually funneled through the cave structures, and that the stairs to access the flanking sides maintain an abstract symmetry.
When bots take the right path, it's now more obvious that the bots are dropping off towards the central path, or continuing with the flanking path. Think about the bots in Decoy, and how they flank along the high route. That's similar to what I was attempting with the varied layout on this side, but still giving the bots the chance to continue with the central path and assist with the bomb.
Finally, just another pretty screenshot of the skybox: