Penetanguishene sits at the south end of Georgian Bay, close to Midland but with a personality of its own. It has marinas and cottage-country traffic, but its deeper story is older: Huron-Wendat presence, French translators and traders, a British naval base after the War of 1812, and a French-Ontarian community that never disappeared.
The town's best sight is Discovery Harbour, where replica ships and reconstructed buildings put the old naval yard back on the bay. The Centennial Museum fills in the local history, while St. James on-the-Lines and St. Anne's Church show the English garrison and French Catholic sides of town.
If you have more time, Awenda Provincial Park is the wild edge of the trip, with beaches and forested trails north of town. Penetanguishene is an easy day from Barrie or southern Georgian Bay, and it clears the bar because its history is still visible on the waterfront.