 Some of Houston's oldest and most distinctive architecture are found in the northern sections of downtown, as the city grew around Allen's Landing and the Market Square historic district, where several representations of 19th-century urban architecture still stand.The Hilton Houston Post Oak (formerly Warwick Post Oak) Hotel was designed by I. M. Pei.Its twin towers are joined by a spacious lobby with a curved glass ceiling that by day lights up the entire space.