This remarkable and remote tunnel in California’s Mojave Desert was the work of a single and very determined man. Gold miner William “Burro” H. Schmidt began burrowing out the passage in 1902 starting from his cabin (which is still there) and going through Copper Mountain in the El Paso range. It leads onto a precarious ledge 4,000 feet (1,219m) up. It took him almost 40 years to manually dig the tunnel, with just the odd stick of dynamite to help blast through the solid rock. What makes the tunnel all the more intriguing is that nobody is entirely sure why he dug it.