The entrance fee was $7 for the day. There were several bathrooms, picnic areas, and a nice visitor's center. The park has plenty of information about activities that you can join on their website and on the information boards that can be found at parking areas. They have a nice website with up-to-date information about activities, several maps, and other good information: Barr Lake State Park website.
Two of their activities included Moon Walks and outings on a Pontoon Boat, both of which I thought would be fun!