The Coast Artillery museum was good, not as good as the Fort Flagler Historical Museum but broader in scope and with interesting artifacts from throughout US military history. The room with information on how Puget Sound, Seattle, and the Strait of Juan de Fuca was defended during WWII and the Cold War is the most interesting part. The museum is within an old barracks, so the space isn't conducive to a typical museum flow, the customer service desk is between the two galleries so you have to pass back and forth to see everything. There was a guided tour of the museum going on, but from what I heard, it wasn't worth spending the time on - the guide was basically just saying what was on the signs, and the tour was barely through the first room by the time I was done with both galleries - and it had already started when I arrived! There is a small entrance fee, and they have books for sale on a variety of interesting military history & local history topics.

Overall, the museum was the highlight of the park, and worth the visit alone. As with any other Washington State Park, you need to have a park pass - which you can buy on-site for $10 for the day, or $30 for the year (and it covers all Washington parks). Consult the Washington State Parks website for specific location, some parks have both machines that take credit cards and a visitors center option, some only have the machines. There is parking outside the museum, but slightly down the road and it does have a time limit.