Any advice? Must sees?

We'll be heading into the area on Friday, probably departing on Monday morn. Have an event on Saturday night, but otherwise open. On the list so far are:

Ballard Locks

Space Needle

Pike Place Market

Pioneer Square, including Klondike Museum and underground tour

Perhaps strolling to the train stations

What else would be good? For that matter, we'll be coming from central CA via I-5, anything good to see on the way? Or another route back?

Feel free to add some ideas.

MV