Pull the blue cord...

...and if you do it'll engage a latch to open the door with. Well, I presume it will as I didn't try it out. The photo is of an alley/ginnel/yard door in Cockermouth, Cumbria, UK.

 

Another image inspired by Rick Olsen's gallery. This is the last plug you're getting Rick - you might demand royalties if I'm not careful... 😀

Done