Expected to cost $1.2 billion to construct, Kingdom Tower will be a mixed-use building featuring a luxury hotel, office space, serviced apartments, luxury condominiums and the world’s highest observatory. Kingdom Tower’s height will be at least 173 meters (568 feet) taller than Burj Khalifa, which was designed by Adrian Smith while at Skidmore, Owings and Merrill. Photograph: Adrian Smith+Gordon Gill Architecture