The Toronto Zoo kicked my ass!
I always found the zoo in the summer to be the most grueling place to visit in the whole GTA. The last time I went in the dead of summer (pre-op), it was hot as hades and I was sweating my arse off. I'd see a building and think "Hooray! Airconditioning!!!", only to be devasted by the jungle-like heat inside those places! There never seemed to be a place to cool down. Glad they have put in the splash pad though- makes a nice spot to get relief.