Great tour! David was our tour guide, he was knowledgeable, enthusiastic and easy to hear. We went below 3 streets and buildings while learning about the history of Seattle. The tour lasts about an hour or a little longer in our case, which was perfect for me.
You do need to be able to walk approx a mile, we walked on the streets and also below, so you need to be sble to go up and down 1 flight of stairs. Also, when underground, they request that you wear a mask. They have masks at the check in desk.