The Maulbronn Cistercian Abbey, Germany (8/418)

Founded in 1147, the Cistercian Maulbronn Monastery is considered the most complete and best-preserved medieval monastery complex north of the Alps. Surrounded by fortified walls, the main buildings were constructed between the 12th and 14th centuries. The monastery's church, built in the transitional Romanesque-Gothic style, had significant influence on the spread of Gothic architecture over much of northern and central Europe. The water management system at Maulbronn, with its elaborate network of drains, irrigation canals and reservoirs, is exceptional.