If you want to celebrate Take the Stairs Day in style, look no further than China"s Tianmen Mountain (literally Heaven"s Door). About 5,000 feet above sea level, the hole in the mountain is the highest naturally formed arch in the world. Originally a cave, it became an arch in 263 CE when the back side of the mountain collapsed, creating the dramatic opening we see today. You"ll have to climb 999 steps to make it to the top, but we promise the view is worth it.