This cathedral, one of the masterpieces of Gothic art in northern France, is unique in terms of its size and unfinished state. Views of the huge 48m-high vaults are head-spinning, while the transept is beautifully lit by stained-glass windows. The astronomical clock, built from 1865 to 1868 by Louis-Auguste Vérité, boasts 90,000 parts, including 50 automaton and 52 faces, which depict the seasons, length of days and nights etc.