The light fixture seems to actually be a window into the bottom of a deep well, with water in it! There is moss on the sides, and a small wellhouse at the top, with a bucket on a string.

You see a way to unlatch the window and open it up - presumably you and this hallway would be drenched in water if you weren't quick to get out of the way. However, do you have some tool to allow you climb up to the top of the well? Yes/No