You can use an action to place this 1-inch metal cube on the ground and speak its command word. The cube rapidly grows into a fortress that remains until you use an action to speak the command word that dismisses it, which works only if the fortress is empty.

The fortress appear as a Dark Hunting Lodge, 20 feet by 30 feet and 20 feet high, with a smoke stack where a nice warm fire is started for the owner. Its interior is divided into two floors, with stairs to the upper floor. When activated, the fortress has a small door on the side facing you. The door opens only at your command, which you can speak as a bonus action. It is immune to the knock spell and similar magic, such as that of a chime of opening.

Each creature in the area where the fortress appears are pushed automatically to the outside edge.

The lodge appears to be made of stone with a wooden roof but is actually made of adamantine, and its magic prevents it from being tipped over. The roof, the door, and the walls each have 250 hit points, immunity to damage from nonmagical weapons excluding siege weapons, and resistance to all other damage. 

The fortress repairs itself with 1 hour of meditation in it's cube form at dawn of each day. The item can only be set up twice per day.

Notes: Utility, Warding