Terry Gilliam was perhaps first to notice the architectural qualities of power station cooling towers, setting the torture scene from Brazil inside the base of one in South London. Their sheer size, monolithic masonry walls and gentle curves make them like enormous castle towers. Particularly special are the ones that have open structures at the base, making them appear to float impossibly, and the view from the inside is what we have focused on in this list. Accidental architectural masterpieces indeed.