In the hills of Ceredigion, Wales, a disused slate mine has become a monument to post-industrial Britain and its afterlives. First opened in 1820 and merged with nearby Braich Goch mine in the 1880s, the Gaewern mine was one of many that contributed to a booming 19th-century export industry that roofed buildings across Europe and the U.S. well into the 20th century. By the 1970s, however, the slate mining industry had collapsed, and locals began tossing unwanted cars, appliances, and household j