I'd be mildly surprised if there was an active gallows today, although for the purpose of the riddle it is possible they were executioners or prison guards. Let us take a guess.
The three men worked at one of those historical villages, as tour guides or something. They decided to take funny pictures. One of the men stuck his head in the loop of a noose at the gallows for a pose. A picture was taken. Blinded by the flash or something, maybe trying to get down, he accidentally triggers the level to make the floor underneath him drop. His neck snaps, and he is dead.