From the City of Toronto Website:

“City of Toronto is proud to present the annual Doors Open Toronto — one weekend, once a year — when close to 150 buildings of architectural, historic, cultural and social significance open their doors to the public for a city-wide celebration.

The program allows visitors free access to properties that are either not usually open to the public, or would normally charge an entrance fee. Many locations have organized guided tours, displays and activities to enrich the visitor experience.”