The fire destroyed about 70 per cent of the main building.
Fire officials believe the fire might have been deliberately set and have turned over the investigation to the police.
Firefighters from the City of Mont Tremblant were called to the scene at 8:45 p.m. Tuesday.
More than 50 firefighters from Mont Tremblant and neighbouring communities were called in to fight the flames.
Nobody was injured in the fire.
Grey Rocks first opened in 1906, but has fallen into a state of disrepair since it closed in 2009.