CN Tower: "Touriste, Touriste" (said with a French accent)
So not quite the hidden gem, but worth a short post. The coolest part of the CN Tower is the glass floor in which many people, including my mom would not dare to walk on. They say its 6x stronger than a conventional floor and it does feel freaky to walk over it while looking down. If you have oodles of cash, you can try the skywalk where you actually go outside and walk around the tower in a harness.