Chicago's skyline rose from the ashes of the 1871 fire, and within two decades the city had invented the modern skyscraper. Daniel Burnham's 1909 Plan of Chicago laid out the lakefront parks and diagonal boulevards that still define the grid today. Louis Sullivan's ornamental terracotta facades and Frank Lloyd Wright's Prairie School principles turned the Loop into an open-air laboratory for American architecture, and the postwar era brought Mies van der Rohe's glass-and-steel International Style to the Illinois Institute of Technology campus and the twin towers of 860–880 Lake Shore Drive. The Chicago River reversal of 1900 redirected the flow away from Lake Michigan, creating the city's drinking-water supply and opening the riverbanks to warehouses, drawbridges, and eventually the Riverwalk promenade that runs from Lake Shore Drive to the confluence with the south branch. The 1920s Prohibition era turned the South Side and Near North neighborhoods into smuggling corridors, and the speakeasy tunnels beneath downtown still surface in guided walks that trace Al Capone's network from the old Lexington Hotel site to the alley where the Saint Valentine's Day Massacre unfolded in 1929. Chicago guided tours today anchor themselves in that architectural and criminal heritage. The Chicago Architecture Center at 111 East Wacker Drive — open Monday through Thursday 10:00 to 17:00, Friday and Saturday until 19:00, Sunday until 17:00 — holds scale models of every major Loop building and rotating exhibitions on urban planning. General admission runs fifteen dollars per adult, and the center serves as the departure point for docent-led river cruises that pass beneath eighteen movable bridges and narrate the evolution of the skyline from the Wrigley Building's white terracotta to the faceted glass of the Aqua Tower. The Willis Tower Skydeck, 110 stories above street level, offers views across four states on clear days, and the Ledge's glass boxes extend four feet beyond the building envelope. Boat tours depart from the Michigan Avenue bridge dock and the Navy Pier terminal, tracing the river's north and south branches past the Merchandise Mart, the Reid Murdoch Center, and the concrete towers of Marina City. Walking routes cover the Theatre District, Millennium Park's Cloud Gate sculpture, and the Grant Park museum campus, where the Field Museum, Shedd Aquarium, and Adler Planetarium line the lakefront in a neoclassical ensemble Burnham himself would recognize.