I grew up in Ossineke, Michigan, and this campsite is a hidden treasure. The beaches here are fantastic, the water is fun to swim in, and the campsites are excellent. There is no entrance fee to the campground area if you just want to come for the day and swim, and there are opportunities for fishing (with a boat launch), hiking, mountain biking, and camping.
There is a water pump for cleaning off sand from your body and feet in the wooded area, and it really is a nice place to bring a camper or a tent for the night (or even a few nights). There are several gas stations in the area for food and supplies, and it's really fun to be out in this area. Sometimes, the white caps get really big if it's windy, so it's a lot of fun.
To me, this is the best feature of Ossineke.