It's a warehouse behind Doctor Doom used for storage. It's called Carnage Warehouse because the HHN house Maximum Carnage (I think that's what it was called) was housed there during HHN in IoA. It's in ReelJustice's pic of the area he posted a few pages back.
Correct and if memory serves it was the only HHN with a video and was the first time the vortex tunnel was used.