We rode it to the end of the current line at Westlake in the downtown Seattle Transit Tunnel, then crossed over to the other platform and rode back two stops to Pioneer Square. Lisa noticed that as part of refitting the system to accept light rail trains in the tunnel, they had to retire the electric bus overhead lines. (Electric trolley buses (ETBs) require two overhead lines. I think it would be difficult to run both ETBs and pantograph-equipped light rail trains in the same line.) This means the buses in the transit tunnel are running on diesel fuel, albeit so-called "clean diesel" and the buses are electric-diesel hybrids whose internal-combustion engines don't run while the buses are stopped.
Exiting the system at Pioneer Square, we walked down to the waterfront, where we had dinner at Ivar's Acres of Clams. It has been some years since I've eaten here. I do like their seafood, and I had a nice mixed grill (prawns, halibut, salmon) while Lisa tackled the Pier 54 Clam Bake (unshelled clams, crab, mussels, and prawns simmered in seafood broth with potatoes). It being Sunday night an hour before their closing time, the place was very quiet, but the staff were nice and they didn't make us feel rushed, the way some places do when it's the end of their day.
We hiked back up the hill to the tunnel and caught the next train south to Sea-Tac, then made our way back to the hotel. My pedometer says that it is almost exactly 1000 steps from the hotel to the light rail station.
So that's another system checked off my list. I'd ride it again if I found myself down by the airport needing to get downtown. Someone attending Norwescon who wanted to spend part of the day at Sakura-Con could make the trip fairly easily, too. That makes two cases of which I'm aware (the other being BayCon and FanimeCon) where there are "traditional" SF/F genre conventions and anime conventions held simultaneously and connected by light rail.