Drive or walk (we recommend walking on- much cheaper and less stressful!) Bainbridge Island Ferry. You can stroll around on the island (it is a bit of a walk to town) and visit the museum or restaurants, or just get back on the next ferry! In our opinion, the ferry ride is the best part- you'll see gorgeous views of downtown Seattle and (weather depending) Mt. Rainier, the Olympic peninsula, and the North Cascade mountain range.
One of our absolute favorite parks in Seattle! There is a two mile walking path along Lake Washington, a beautiful old growth forest, and, on a clear day, stunning views of Mt. Rainier.
This is another of our favorite parks! There is a nice walking path that goes from the marina to the end of the beach with beautiful views of the Olympic Mountains.