Sweaty in December

I was wondering if I should let you guess what I blipped today, but gave up on the idea.

When I get off the train I have to use a tunnel undergoing the tracks to get to the parking lot and my car.
For some reason I looked up today: The ceiling of the tunnel was covered with water drops! All over the ceiling! Sweating concrete...

It was one of the situations when this blipper waits until everybody is gone, before taking out the camera to take a photo of a sweating tunnel ceiling.

18:40; 10°C