The Underground Storage was an area next to the A Bizarre Building, where there is an underground building which leads to the a black backdoor, leading to the Underground Storage room.
To enter the storage room, the player needs to have a stand that could teleport through walls. The storage room also replaces the Tom's Juice Shop, which has been deleted.
This Storage is also near the sewers, which is also located in the Underground space. As of today, there is no explanation as to why this room exist, as there is nothing unique included in this room. The only explanation could be for aesthetic purposes, with boxes and a painting between them.
The Underground Storage appeared as a simple storage room with sets of paintings and cartboard boxes. Near one of the boxes, Stand Discs from Whitesnake were located on the floor. One of them, had pictures of unreleased stands.