Strange Door...

In an underground station, I stand on the platform opposite a door.  Around the door is rough concrete with exposed metalwork, as if this door has recently been opened through the wall of the tunnel - or given that none of the structure looks new, perhaps crudely re-opened.

What is it for?  There seems to be no way to reach it from this side unless you open the doors on the "wrong" side of a stopped train.  I checked though, this doesn't appear to line up with the doors of a train when stopped.

Intriguing.