Aldersea Day Spa

This small building is occupied by super mutants and their hounds. In the lobby, there's an advanced door in the corner, near the counter. There's an advanced-locked safe there, a handful of chems, and a duffle bag behind the chaise.

Take the stairs going down and defeat the warlord and his hound in the pool area. You can loot the Spa Key from the warlord's body. Don't forget to loot the red steamer trunk in the sauna room as well.