The Oculus Pavilion

Abandoned art installation/public washroom facility along the Humber Trail. The roof has a very cool reverberation effect, try standing in the middle and yelling really loudly (bonus points if its sunny out, so you can stand right in the spotlight).   

From an urbantoronto.ca article:

Cyclists and pedestrians taking a casual stroll along the Humber River Recreational Trail have for years been greeted by a rather fantastical, if not jarring site. Perched next to the trail in a secluded meadow surrounded by trees in South Humber Park, the Park Pavilion (commonly referred to as the Oculus Pavilion, or just the Oculus) stands as an understated monument to Toronto's mid-century concrete Modernist era. Designed by architect Alan Crossley and built by Toronto Parks in 1959, the whimsical canopy and fieldstone structure once housed public washrooms that have long been shuttered and left in abandonment.

The pavilion originally featured a dramatic sculpture at the centre of the oculus, perfectly framed by the circle of sunlight - an integral component that is regrettably missing today. The stone base on which the pavilion sits is now dotted with weeds sprouting in between the cracks, while the slender steel columns, once a gleaming white, have since been painted a deep rusty red.   

https://urbantoronto.ca/news/2016/07/oculus-future-uncertain-south-humber-parks-hidden-modernist-gem