This was kind of a cool place to explore back in November last year. My dad lives on Whidbey Island and his wife gave us a little tour around Fort Casey, which is a Washington State Park and historic district. It was really cool getting to see old historical bunkers and how they form into the landscape. We didn’t get to explore much of the grounds, but from what I gather, on a sunny day this place looks awesome for a picnic. The park boasts of 999 acres of land so there is definitely a lot to explore.
For those visiting Seattle, I would recommend doing a day trip to one of Washington’s surrounding islands. Whidbey Island is a cute Navy town, but there are others like San Juan Islands or Orca for whale watching and/or kayaking.