Bolt from Portland to Seattle
Not quite public transit, but a bus adventure nevertheless. BoltBus.com is running an express bus between Portland and Seattle. It leaves Portland at 6th and Salmon (across from the Hilton and next to Starbucks) and arrives in Seattle at Union Station (5th and King St). Both are great locations for catching public transit to get to your final destination. The is a big comfy tour-style bus, with lots of leg room, overhead bin, reading light, electrical outlet and wi-fi connection. There is also cargo space for luggage or whatever. In three hours, you are in Pokies a new city! The prices are inexpensive, but they do vary by time. I paid $28 for the round-trip ticket.
It was fun to visit friends in Seattle and easy enough to catch public transit back to Union Station in Seattle–it seems like most buses stop there. It is by the International District. In Portland, the Bolt stop is near the 6th and 5th Avenue bus transit strip, so it is no more than a couple of blocks to most of the buses passing through downtown Portland.
Check it out at:Bolt Bus