One of the most famous landmarks in the world was, at the time of its construction for the 1889 Exposition Universelle, also the tallest building on earth, at 1,063 feet high. Before its opening, plans for the structure were met with scorn. Notable artists including Guy de Maupassant and Paris Opera architect Charles Garnier even signed a letter in Le Temps that called it a "dizzyingly ridiculous tower dominating Paris." Still, Gustave Eiffel, an engineer by trade, persevered, and on the day of its opening he climbed the 1,710 stairs to unfurl the French flag at the summit himself... (Photo: courtesy tour-eiffel.fr)

The Palace of Fine Arts
1893 World’s Columbian Exposition; Chicago

The Buckminster Fuller Dome
1967 World's Fair; Montreal, Canada

This 200-foot-high geodesic dome was designed by Buckminster Fuller (the inventor of the shape) to house the U.S. Pavilion. This was his most complicated yet: Three-dimensional shapes called icosahedrons, which are 20-sided figures composed of sturdy equilateral triangles, were required to support such a large structure. The U.S. donated the dome to Canada in 1967, and now it houses the Environment Canada biosphere in Montreal. (Photo: CCWE / Expo67 Foundation / Coll. Georges de Passillé)

The Millennium Dome
2000 Millennium Festival; London, England

Located right on the prime meridian and in the home of Greenwich Mean Time, London's Millennium Dome fittingly resembles a clock, with 12 yellow masts sticking up out of a gleaming white "face". (Project director Mike Davies was into astronomy, so the number 12 also references the months of the year and constellations in the zodiac.) (more here)(Photo: Sergio Pitamitz/CORBIS)

The China Art Palace
2010 Expo; Shanghai, China

Like other World's Fair structures, the iconic China pavilion of the 2010 Expo has taken on a second life as an art museum — a really, really big one. The China Art Palace has more than 160,000 square meters of exhibition space covering five floors. One of the Expo highlights, "Along the River During Qingming Festival," a digitally animated rendering of an ancient scroll, is still on exhibit within. (Photo: courtesy Knippers Helbig).