Thanks everybody for your interesting comments on this one.
In the viewfinder it was the lines/shadows that appealed to me but when I got it home and looked at the bigger picture, so to speak, I found it a bit menacing especially with that trapdoor at the top. I sort of imagined myself coming to the end of a search but with a sinister outcome. Sometimes burnt out highlights can destroy a picture, (they have on a lot of mine anyway) other times, if your lucky, they can be an absolute asset. In this case the extreme highlight added a graphical element that fitted in with everything else, I think.