There's just one elevator. And it likes to take trips by itself, especially at night; especially to the roof without the special key necessary for a rooftop stop.
The culprit is...
Stephen Durwood Hoag inherited the hotel from his father and managed it for almost fifty years.
Hoag enjoys playing pranks on patrons in the Riverfront Bar and, late at night, his spirit roams the third floor, where he lived.