Molly's Key, Control Room and Maintenance Room Doors

Molly, an NPC trader in Slatten Dale, sells a "Concrete Shelter Key" which opens an alternative, but ultimately unnecessary, entrance to the Sewer Tunnels. This key is not recommended as it offers no significant advantage over other sewer entrances.

To access the maintenance room, you must first reach the control room. The control room cannot be accessed from within the Sewer Tunnels.

Exit the Sewer Tunnels into Casterfell Woods.

Locate the elevated highway running north-south through the center of Casterfell Woods.

Find a way to get onto the highway. If you exited the sewers nearby, follow the stream north until you find a red telephone booth, then follow a trail north and northeast that switchbacks uphill to join the highway.

Follow the highway south until it ends at a collapsed tunnel.

Look to the left (southeast) of the road for stairs leading up to a doorway.

Enter this doorway to access the Sewer Tunnels behind the locked control room door.

From your entry point, head south, then east down some stairs, then south up another flight of stairs to reach the control room.

Search the southern end of the control room to find a body containing the note "Keep the Interchange Dry" and the essential Sewer Tunnel Key.

With the Sewer Tunnel Key in hand, exit the control room to the east.

Continue east on the catwalk and descend a ladder to return to the restricted chamber in the lower level of the sewers.

Head west and follow the maintenance signs west and south down some stairs to find the locked maintenance room door.

Use the Sewer Tunnel Key to open the maintenance room door.

Inside the maintenance room, head to the southwestern corner and squeeze between crates and shelves.

To the south, you will find a B.A.R.D. Crate containing a Training Stimulant and other items.