Since the beginning of civilization, humans have paid homage to the spiritual realm by erecting beautiful structures on Earth. In this program, Dan Cruickshank visits Saint Catherine's Monastery in the Sinai desert, built where Moses is said to have received the Ten Commandments; China's Hanging Temple, a Taoist monastery that clings precariously to the sheer face of a cliff; two 16th-century wooden churches in the Russian wilderness that still serve...