Annett Nature Center in Warren County has several hiking trails, an observation tower and pond. The trails aren't marked, so I recommend printing or downloading the trail map ahead of time because my cell reception was very poor there. One of my kiddos led our hike and did a great job following the map.
The observation tower provides a great view and is definitely worth climbing.
There are two large shelters with picnic tables. One near the nature center, which also has restrooms, and one near Lester Pond, which is a short walk from a pit toilet.
After our hike, my boys enjoyed participating in the annual Mud Day event, which happens each year at the end of June.