http://www.nytimes.com/2013/12/20/us/under-seattle-a-big-object-blocks-bertha-what-is-it.html?_r=0
http://gizmodo.com/something-called-the-object-has-stopped-worlds-large-1487090414
http://www.coasttocoastam.com/article/seattle-s-baffling-underground-object
http://www.wsdot.wa.gov/Projects/Viaduct/About/FollowBertha,
http://www.flickr.com/photos/wsdot/collections/72157607634023054,
http://www.flickr.com/photos/wsdot/sets/72157631528692308
This is a big transportation pipe.
http://www.flickr.com/photos/wsdot/4907983170/in/set-72157631528692308
When the Downtown_Seattle_Transit_Tunnel was built, there didn't seem to be any underground anomalies. http://en.wikipedia.org/wiki/Central_Link#Stations
The Beacon_Hill_station is perhaps the deepest in Seattle so far.
http://en.wikipedia.org/wiki/Beacon_Hill_Tunnel_(Seattle,_Washington)
