The lovely brown colour is dirt! This is a passenger tunnel that links Knott Mill Station to G-Mex Metro stop. Suffers a bit because of the way its constructed, it can never get cleaned ,very similar to the Arndale bridge, click here to see it. http://maxblack.shutterchance.com/photoblog/36410.htm

Tried a cod HDR thingy on this by duplicating the original twice, using a shadow highlight on one, levels on another and leaving the last alone, then just blend with a soft brush through a mask, probably try this again! Once I worked out  what and when to do it took about 5 minutes, need to buy more hot cross buns to fill the time void.