Is there anything I should be sure to see while I'm near Seattle?

I’m going to Ft. Lewis for surgery the last week of May. I have 2 days where I don’t really have anything to do, except for an early morning pre-operative appointment. I will be pretty close to Seattle and have a rental car. Is there anything I should be sure to see while I’m there? I will be traveling alone, so preferably stuff that’s safe to do alone.