Entrance to the Seattle Underground Tour in Pioneer Square http://pnwtravels.hubpages.com/hub/seattle-underground-tour
The Underground tours!!! So cool and spooky. Not sure about this particular company, but in general totally worth doing. Underground opium dens, prostitution, speakeasies and shanghaiing (see : http://en.wikipedia.org/wiki/Shanghaiing).
Tour of the city under Pioneer Square-Seattle
The Seattle Underground Tour http://www.squidoo.com/seattle-underground-tour
London Underground - Clapham Common Tube Station, London, England
Mercat Ghostly Underground Tour: Edinburgh Vaults. Things to do in Edinburgh, Scotland #review
The U.S. Capitol Building is an icon that's open for weekday tours.
Pioneer Square – Gateway to the Underground Tour -Seattle - # 5 of 5 Part Series
Wow! Why can't the U.S. put this much effort in making out country beautiful! These are Moscow metro stations, a public service building, and they look fantastic!