Seattle's Lake Union and Fremont Troll bus
 

how to go from Seattle downtown art musem area to Seattle's Lake Union and Fremont Troll by bus ? I used google, it is hard to get. Thx.

Take a look at the King County transit planner. If you can come up with locations (intersection, address) it should be able to give you bus schedule information.
http://tripplanner.metrokc.gov/cgi-b....pl?resptype=U

Walk to 3rd and Pike (a block from the Museum) and take the no. 28 bus to 34th and Fremont (just over the Fremont Bridge.) Then walk (steep hill) to the troll on 35th right under the Aurora bridge.

As for "Lake Union," it's right underneath said Fremont Bridge. But it's a big lake so where on Lake Union is another matter. Because of the Ship Canal, using public transit around the periphery of Lake Union is quite challenging. Walking is easier, but there can be some very long schleps.