One of the more unpleasant tourist attractions in Seattle is the gum wall.  That made it on to the blog in this post from a few years ago.  We went to check it out when we had visitors staying recently.  However, we had chosen poorly (or well depending on your perspective).  They were in the process of cleaning the wall.  Some poor guy was busy with a jet washer blasting the crap off the walls.  Not a nice job I imagine.