It's impossible to imagine staying in Beijing without a trip to see the Great Wall, the largest manmade structure on the planet. Winding over thousands of miles, the wall follows every contour of the land it traverses, but it is at Simatai, where it straddles vertiginous ridges, that it takes on its most extraordinary appearance. Choose one of six departure points, depending on whether you want a quick look at the wall or a more challenging hike along this stone structure thousands of years old, which follows the border between China and Inner Mongolia.