A moulin is a narrow, tubular hole in a glacier through which water enters from the surface. It is also a word for a type of windmill.
Moulins are important in understanding how glaciers work and can be dangerous to people exploring glaciers.
Examples:
The moulin in the glacier was very deep.
The water rushed into the moulin.
The moulin was like a big hole in the ice.
The moulin was so deep, it felt like falling into the sky!
The moulin was as deep as a hundred houses stacked on top of each other.
The wind turned the moulin and made power for the town.