The quest to unlock Deepholme will trigger when you go to Deepholme after having completed the heist quest Shadows of One's Past and set up the Explorer's Society. After The Vaults of Deepholme quest has finished, Deepholme itself will become available as an off-site storage for powerful artifacts and magic items, while replicas can stay on display in the museum without being at risk of another heist.
A few of the new Society Guards will protect Deepholme and its surroundings.
The items can be displayed by placing them in the appropriate sorting chests. Once displayed they can either be taken from their display spots or directly back from the chests.
On the far side of the large hall is the Daedric room. On a platform above a lava pit secure behind multiple gates and the draw bridge.
The upper three rooms on left side of the hall feature the Weapon Displays. all three rooms have a weapon chest, the chests are linked together and display the weapons in whichever of the three rooms the weapon goes to.
The upper three rooms on the Right side feature Armor Displays, Again the chests are linked together and display the items across the three rooms.
In the XY room is a Jewelry Display case, a small strongbox serves as the auto-sorter for the rings and necklaces.
The bottom third room on the left (from the entrance) features a display for the three [[Deepholme - Elder Scrolls Room|Elder Scrolls.
The bottom second room on the right has displays for the Black Books Room.
The bottom third room on the right features a large display for dragonpriest masks (could be more then just those) Deepholme - Masks Room
In order to enter after the quest, the Totemic Key is required to lower the gate.