A panoramic view of the gravel pit near Kongensbro, Denmark, which is operated by BG Stone. Gravel pits are open-pit mines for extraction of gravel and often lie in river valleys where the water table is high. As such, pits may naturally fill with water, and abandoned ones are often used as nature reserves or as amenity areas for water sports, landfills and walking.Photograph: Slaunger; edit: David Iliff