Lake on the Mountain in Prince Edward County is about a five minute drive from Picton on the way to the Glenora ferry. It's a great half hour stop (unless you happen to be having your lunch or dinner at the Lake on the Mountain Resort - a fabulous restaurant that serves some of the great local Prince Edward County wines), in which case I'm sure you'll be staying a bit longer.
Lake on the Mountain is a natural oddity that sits 203 feet above the Bay of Quinte with no visible source of the water. The Mohawks believed the lake was bottomless and used to offer gifts to the spirits here, as they believed it was a sacred place where the three sisters, Corn, Squash and Beans lived. I'm not sure how they came to that conclusion, but the place certainly has an odd feel to it. The lake must be fed by a groundwater source, but the source has yet to be discovered. All kinds of theories have sprung up about this lake, but in all probability it is just a giant sinkhole.
What makes this location especially strange is how it can fool your senses. If you happen to be standing in a particular spot you can see the lake in front of you, and out of the corner of your eye you will be able to see the Bay of Quinte 200 feet below. It's rather strange seeing two bodies of water at such different elevations simutaneously. There's a parking lot right beside the lake, and many people stop their cars and watch the Glenora ferry operating 200 feet below.
Lake on the Mountain is actually a Provincial Park. It's a very small one though, made up of about 250 acres, the vast majority of it being the Lake itself. There is a very small boardwalk, some picnic tables and restrooms, but that's really about all there is to it, nature takes care of the rest. Motorized boats are not allowed on the lake, but many people have cottages and homes around here, and I often do see people fishing (how the fish got into this lake, I'll never know), sailboarding, and other water activities that don't require a motor. If you are driving through the "County", Lake on the Mountain is definitely worth a look-see.