It is an old, desolate house. The shack is inaccessible from the outside before starting the quest "With Friends Like These...", as the key is needed to enter the shack.
The Dragonborn is taken here by the Dark Brotherhood after completing the "Innocence Lost" quest and receiving a Mysterious Note from a courier. The key required to leave the shack is received after completing "With Friends Like These..." or "Destroy the Dark Brotherhood!".
The Dragonborn will meet Astrid who commands them to kill one of the three victims in the shack (Fultheim the Fearless, Alea Quintus, or Vasha). The choices are to follow her command and receive an invitation to join the Dark Brotherhood.
Alternately, attacking Astrid instead of killing a victim will initiate the quest "Destroy the Dark Brotherhood!".
- Should one return to the shack at any time, the surviving NPCs will still be there.
- Items stored in the chest and drawers are not safe for storage and will respawn after a few days.
- It has been speculated that this might be one of the possible locations in Skyrim in which the books The Woodcutter's Wife and The Cabin in the Woods take place.