Sorry, but the Seattle Underground Tour only operates during the peak summer vacation months.
Basically, Memorial Day weekend, through Labor Day weekend, (last week in May, through 1st week of Sep).
I looked at the schedule in the link, but that has not been my experience. Better call for accuracy.
Great 'street photo' ops along the Pier walk. Pike Place Market was mentioned, too.
Good weather or bad, I could spend a day or two, shooting pictures at those nearby water front attractions.

