The route they use is pretty good for indoor runs when the weather or slush/ice gets bad. Mix of stairs + flat stretches. The only downside is that parts of the route are gated by doors which you have to open manually, but def a first world problem.
Plus, like any other person using the PATH, the runners got lost along the way.
see https://runningmagazine.ca/the-scene/torontos-underground-5k...