Toronto Police Constable Wendy Drummond told the Toronto Sun an emergency call came in just before 2 a.m. that a woman had fallen into an interior courtyard.
The unidentified 29-year-old victim had no vital signs and was later pronounced dead at a nearby hospital, the Toronto Star said.
Police said she and an unidentified man were trying to jump from one quadrant of the 134-year-old Gothic-style building to another. The man made it, but the woman didn't.
"They were believed to be exploring an old building because it's rumored to be haunted," Drummond told the Sun.
It wasn't immediately known if the two were students, and police said they were trying to determine how they gained access to the building at that hour.
Both had been drinking, police told the Star.