Built in: Mayor Richard M. Daley's vision in 1997 to transform unsightly railroad tracks and parking lots by extending Grant Park was quickly reconceptualized into a milestone park for the new millennium. The grand opening ended up being a few years into the millennium in 2004.
Built by: Skidmore, Owings & Merrill crafted the Beaux-Arts master plan unveiled in 1998, but it underwent numerous changes with architects like the park's appointed Project Design Director Ed Uhlir and Frank Gehry involved.
Why it's one of the seven wonders: Millennium Park is the city's latest modern-day wonder, and comes in just behind Navy Pier as Chicago's most visited tourist attraction. Stretching nearly 25 acres just north of the Art Institute of Chicago, the park covers a portion of rail yard and two parking garages as one of the world's largest green roofs. Drawn in by architect Frank Gehry's involvement with designing a sculptural music pavilion with a huge, steel trellis sound system and serpentine pedestrian bridge, the park is filled with the work of notable 21st century artists like Anish Kapoor's mercury drop-inspired "Cloud Gate" sculpture mirroring the cityscape and Spanish artist Jaume Plensa's eccentric, 50ft water fountains with video projecting the faces of everyday Chicagoans. The ambitious park ended up with years of delays and a whopping $475 million dollar price tag, but Grant Park's expansion continues with the nearby Maggie Daley Park riding on Millennium Park's success.