"Hidden" perhaps if you're a city dweller: St. Edwards up near Kenmore (20-25 minute drive north) is a huge elaborate dream come true for any 6 year old and there's a gorgeous wooded hiking trail too.

I don't know if it's hidden, but I'm surprised at how many people I talk to have not been to Ravenna Park. I grew up near it, and it's still my favorite Seattle park. Lots of little streams, with tiny bridges, and small footpaths that branch off up the ravine. It's super busy metropolis-y everywhere around it, but through the middle, it's peaceful. It does get awfully muddy in the winter, however. We only go there right now when we feel in the mood for a good mud puddling.

Bhy Kracke Park in Queen Anne. It's not just fun to say, it's fun to do. 434 Comstock Place. Great view. There are probably some goldfish crackers buried in the grass from a picnic I had in August 2008. You can have them.

Bhy Kracke is awesome. First park I stumbled upon when i got to seattle in 93 and was looking for a place to walk the dog after a long drive from Jersey.

My favorite unknown park is Deadhorse Canyon which is part of Lakeridge Park in way south seattle at the border with skyway. It's got old growth trees, a nice creek with cutthroat trout (hard to find, though) and a great trail with a couple of awesome bridges. I've been involved in the restoration effort their for over 10 years and I'd swear only a handful of people ever use it. Very good birding.