Directions
The Museum of Flight is near the south end of Boeing Field (King County Airport), which is about 6 miles south of Seattle. Some directions and a live version of the map above can be found on the Museum's directions page.
More complete instructions on how to get there
Coming from NORTH of Seattle: Get on southbound I-5. Take exit 158. This dumps you out at the Boeing Access road. Take right, and head westbound about a half mile. This gets you to East Marginal Way (called that because it's on the east side of the Duwamish Waterway). Take a right onto East Marginal Way, and go northbound about a half mile. The Museum is on the right. Just before you get to it, there's a huge ugly whitish building on the left. That's the Boeing Developmental Center.
Coming from SOUTH of Seattle: Get on northbound I-5. Take exit 158, going beneath an underpass that leads to a cloverleaf that rotates you 270 degrees to the right. (For all you math types, that's isomorphic to a 90 degree left turn.) The clover leaf puts you onto the Boeing Access road westbound. Go about a half mile. This gets you to East Marginal Way (called that because it's on the east side of the Duwamish Waterway). Take a right onto East Marginal Way, and go northbound about a half mile. The Museum is on the right. Just before you get to it, there's a huge ugly whitish building on the left. That's the Boeing Developmental Center.