The Harbormaster Hotel is a very small area consisting of the main hotel lobby, and room 61 on the 6th floor (all of the other rooms are blocked off) and the hotel roof, guarded by some raiders.
After taking the elevator from the lobby, opposite the exit is an Advanced locked door. Behind this door is an unusual scene: the skeleton of someone sitting in a chair holding an overdue book, while surrounded by a Giddyup Buttercup wearing a bowler hat and "smoking" a cigar, a Jangles the Moon Monkey wearing a sea captain's hat and a teddy bear holding a baby rattle while inside of a plastic pumpkin perched on top of an overturned trashcan.
The Harbormaster Hotel appears only in Fallout 4.
Behind the scenes
The Harbormaster Hotel is based on the real world location of the Boston Harbor Hotel located on Rowe's Wharf, geographically similar to the in-game equivalent.
Several items in the lobby downstairs (a clean cup, clean glass, glass pitcher, undamaged camera, unused ashtray, Fancy Lads Snack Cakes, and a preserved cigarette pack) are all incorrectly marked as stealing.[verified]