Museum of Flight
The name tells you right away whether you personally will find this interesting; at minimum, it will get you inside on a rainy day. The collection includes 131 aircraft and spacecraft ranging from wood and fabric crates to the SR-71 and, parked right in the front parking lot, a sleek Concorde. Don't bonk the landing gear with your car door!
Western Bridge
While it may seem a odd location for a modern art gallery, amid the light industrial and retail sprawl the makes up the bulk of Sodo and a stone's throw away from Qwest and Safeco fields, perhaps it isn't after all. They make great use of warehouse they came to occupy, never changing anything to take away from the fact it is a warehouse. They host museum quality exhibits and, especially for this neighborhood, a unique, cultural outing.