The Grotto is a big cave on the shore of @explorethebruce's Bruce Peninsula National Park that was carved out by the waves from Georgian Bay. We reached it by climbing down the "rabbit hole", a tiny tunnel from the ground above. The water inside glows a bright turquoise from the sunlight streaming through an underwater tunnel that leads to the Lake outside. Would you jump in?
There are a couple of caves along the edge of the Lake in Bruce Peninsula National Park--one of which being the Grotto, where you can swim into (also where I dropped my camera yesterday, haha) and back out through a smaller underwater cave. I really liked this smaller cave next to it, where I could climb down into and peek out over the Lake.