One extra for Challenge Blue

I took this picture for Challenge Blue. Initially, it didn't make the cut for pictures to be posted, but I keep coming back to it, because there's just something about it.

To be honest, I'm not entirely sure what it is about this picture that grabs me. Maybe it's something raw about having an emergency button on this "rough" basement wall - yes, it's all painted white, but there are lines for .. power?, cut outs for access doors, and electrical boxes all over the place. Things that would normally be hidden, are acceptable in the tunnels under the city. And then there's this sharp blue - bold, clean, clear that just stands out against all the white. (As it should, for an emergency button!)