What is the weather door?

If you want to get to the very top of the spire, you have to go outdoors at some point.

375′ or 114m above the ground is as high as you can go inside the spire, and at that point you have to climb through a very little door on the north side of the spire.  It’s just above the third decorated band, on the north side of the cathedral, and can clearly (if microscopically) be seen in the usual picture that everyone takes.  To add some variety to your life, here’s a picture at night with the door indicated.

The Salisbury Journal have kindly published a picture of it being used, which might make a fun caption competition:

Possible questions inspired (ha ha) by this might include:

Did people historically climb the spire?

How do you get to the weather door?