A forgotten but not-so-secret city wound its way under my feet in Seattle. I didn’t know it existed, but my first hint that something lurked below was the small and thick amethyst-hued squares of glass embedded in the sidewalks around Pioneer Square. I found myself wondering what purpose they served. When I discovered that they were skylights for an underground city, I simply had to know more. Fortunately, there’s an exceptionally popular tour that explains all the mysteries. Read more >