Try to get a bike from someone. Best rides ever-
-burke gilman to golden gardens. Watch the sun set, have a bonfire. Get drunk, and hit on randoms. Make sure they don't go to Ballard. If you have time to kill during the day, swing over to carkeek and wander around there for a while.
-greenlake to alki.
-burke gilman around the lake to microsoft, bus back via the floating bridge.
-ballard locks, discovery park, golden gardens, in whatever order you feel like.
-Start at Mathews beach, bike down the west side of the lake, and swim at every beach you pass. Theres a bunch of them and its a perfect flip flop kickin it kind of ride. Hipster clothing is essential.
My go to summer things are basically Golden gardens, Paseo sandwiches, alki, greenlake, and UW canoe rentals.