It's a pretty rare thing to find a swimming pool in a national park. Pinnacles is one of those rare parks that actually have a swimming pool and it's a great park to take a dip!
Bear Gulch Nature Center is a great spot to get acquainted with the things to do at Pinnacles National Park. The nature center holds all sorts of information including park maps and helpful rangers.
Pinnacles Campground is a great (and only developed) spot to spend the night in the park. The campground even has a swimming pool (a rarity for a national park - more on that below).
One of the park's top attractions is watching the endangered California Condor in it's native habitat. This is an impressive bird (albeit not the prettiest) that is a true sight to behold.
High Peaks Loop is probably the most popular trail in the park giving hikers the most famous views of Pinnacles including the rock spires you see in the photos.