Orillia sits between Lake Couchiching and Lake Simcoe, close enough to Toronto for an easy break but far enough north to feel like the start of cottage country. It is not grand, but it has a real day out in it: a lakefront boardwalk, a good small museum scene, a handsome opera house, and the memory of Stephen Leacock's fictional Mariposa.
The waterfront is the easy pleasure. Couchiching Beach Park and the port give you lawns, beaches, boats, and a boardwalk that make the city feel more open than its downtown grid suggests. A few blocks away, the Orillia Opera House and the Orillia Museum of Art and History keep the old civic core interesting.
The best single reason to come is the Leacock Museum, set in the humourist's former summer home at Old Brewery Bay. Add the Mariposa Folk Festival if your timing is right, and Orillia becomes more than a highway stop on the way north.