14,197 feet (Everest)

Mount Everest stands at 14,197 feet above sea level, which is roughly equivalent to climbing almost 2.7 miles into the sky. To put it in perspective, if you flew in an airplane, you'd reach this altitude as part of a high-altitude flight. It's higher than the tallest building in the world, the Burj Khalifa in Dubai, which is about 2,717 feet tall—I’d need to stack about five of those buildings end-to-end to match Everest’s height. This elevation is so great that oxygen levels are significantly reduced, making it a challenging environment for climbers.