Bradt was introduced to rock climbing by Gustave Gambs (1868-1958) who had learned the sport in Europe. He soon became an active proponent of rock climbing, introducing many people to the sport, some of whom became leaders in the field, such as Don Hubbard, Arnold Wexler, and Herb and Jan Conn. Bradt and his colleagues explored and developed early climbing routes at Great Falls, VA, Carderock, MD, Seneca Rocks, WV, Old Rag Mountain in Shenandoah National Park, VA, and in the Teton Range.