On walks in the Cedarvale Ravine, near Spadina, I’ve noticed a circular entranceway with doors leading into the hillside

Nothing quite so picturesque. Built in 1975, those doors actually give way to an emergency subway exit—a concrete staircase that descends to one of the deepest sections of track in the entire system. The exit has only been put to use once, on the fateful evening of August 11, 1995, when two trains collided just north of Dupont station, killing three passengers and injuring about 36 others. As temperatures in the tunnel soared to more than 40 degrees Celsius, rescue workers (there were more than 200 on the scene) relied heavily on the emergency exit to ferry gear down to the wrecked trains and to evacuate passengers. If it hadn’t been for those well-placed hobbit doors, Toronto’s worst-ever subway disaster could have been even nastier.