Blake Island is a jewel. It is far away from Seattle, yet it is right in Seattle's back yard. All of Blake Island is a Marine Park; it is inaccessible except by boat. For the non-boating public of Seattle, it is far away, yet once you are there, the Seattle skyline is the whole eastern horizon.
For those in Seattle who do not have marine transportation, the m/v Goodtimes (and perhaps other Emerald cruise boats) will take you from downtown to the Indian longhouse on the NE corner of the island for a unforgettable meal of salmon cooked at an open fire and native dancing and culture.
There is a tiny marina at the NE corner where the cruise boats dock, but which can accommodate a few additional boats for overnight moorage as well. And the island is ringed with State Park mooring buoys, for those who wish to avoid the hustle and bustle of the little marina (um, that would be us).
We have used the buoys on the East side and those on the West side. None are immune to the roll which comes from the wakes of the passing shipping, or the ferries, but perhaps the West side is a little calmer. There is a "mooring cable" arrangement on the West side, but we avoid these things like the plague (I'd much rather anchor).
The whole island is threaded with hiking trails which take you thru deep northwestern woods, all ending on sandy beaches. Eagles soar overhead, and the interior is primally quiet. There is much to explore, and boating families with children enjoy Blake Island for just this reason. (Apologies to Scott and Angela of Ghost, as this is their favorite anchorage - guys, if I got this wrong, please fix it in the comments!)
The far northwestern tip of the island is a lovely sandspit which is a designated kayak/canoe primitive campground. I think it would be really fun to take a kayak onto the Southworth ferry from Seattle, and launch it at Southworth with this campground as a destination. It would be a protected mile long paddle with a great endpoint.
Legend says that Blake Island was the birthplace of the Suquammish Chief Sealth, for whom the city of Seattle was named. More recently, the entire island was owned by one Wm. Trimble. He built a reportedly beautiful mansion on what he called "Trimble Island", but abandoned it in grief when his wife was tragically killed in a freak accident in 1929.
Eventually, the mansion burned. Recently, family of a long-gone great uncle revealed that he and a companion sheltered in the mansion after losing their boat in the icy waters of Puget Sound. They started a fire in one of the fireplaces, which perhaps had a defective chimney. They left the island, not knowing that a smoldering ember had initiated the demise of the mansion.
Few signs remain.
Walk the beaches, walk the trails, and realize that few cities in this country have such a jewel so close, and yet so far.