Turner Falls is one of the most beautiful parks in the state, unfortunately, it's owned by the City of Davis and they're a little bit greedy when it comes to admission. Keep in mind when you're thinking about booking that your reservation price will also include the park access for each person/vehicle in your party. It's a little bit convoluted but they do disclose it if you dig around on their website.

Collings Castle is an extremely cool and pretty unique hike, especially if you're into abandoned places. It can get pretty crowded but there are plenty of nooks and crannies in the maze of buildings that you can duck into. Some folks think it may be haunted and I don't usually buy into stuff like that - but anyone who built a castle during the Great Depression probably had a few skeletons in their closet. 

The falls are obviously stunning but the caves are a must-visit if you can find them. There are tons of secrets to find and natural mazes. Despite my issues with the ownership, Turner Falls is always worth a trip.