So many great things to say about Big Bay state park. This park is located on Madeline Island, the biggest island in the Apostle Islands. 

I have been to this park more than once. It isn't the easiest to get there (you need a ferry ticket or chartered boat) but you can  take your car or RV on the ferry (RVs generally need a reservation ahead of time depending on size). 

If you are not taking a car, you can rent scooters or bikes (or bring your own). If camping, you will want to bring your car to drive to the park. It is a 7 mile ride to the park located on the other side of the island. Make sure you have your annual park sticker (or park pass confirm) when headed there. 

The park has beautiful hiking trails along the coast, a swim beach (water is cold!!), Kayak and SUP rentals for bay paddling. 

The modern bathrooms were decent (vaults are cruddy). The campsites are nicely wooded. Since the island is small, you can explore all of it on a three day weekend, whether that is hiking, paddling on the interior of the island into backwaters (you may see black bears on the shore).