Extracted from the Wikipedia article World's fair.
Remaining structures
1851 – London: The Crystal Palace, from the first World's Fair in London, designed so that it could be recycled to recoup losses, was such a success that it was moved and intended to be permanent, only to be destroyed by a fire in 1936.
1893 – Chicago: The Museum of Science and Industry in Chicago is housed in the former Palace of Fine Arts, one of the last remaining buildings of the World's Columbian Exposition. In conjunction with the fair, the Art Institute of Chicago building was built to house conferences, as the World's Congress Auxiliary Building. The Garden of the Phoenix, a remnant of the Japanese pavilion, also survives. The intent or hope was to make all Columbian structures permanent, but most of the structures burned, possibly the result of arson during the Pullman Strike. The foundation of the world's first Ferris Wheel, which operated at the Exposition, was unearthed on the Chicago Midway during a construction project by the University of Chicago, whose campus now surrounds the Midway. Relocated survivors include the Norway pavilion, a small house now at a museum in Wisconsin, and the Maine State Building, now at the Poland Springs Resort in Maine.
1906 – Milan: The Civic Aquarium of Milan built for the Milan Exposition is still open after 100 years and was recently renovated. The International Commission on Occupational Health (ICOH) was settled in Milan during the fair and had its first congress in the Expo pavilions. In June 2006 the ICOH celebrated the first century of its life in Milan. An elevated railway with trains running at short intervals linked the fair to the city center. It was dismantled in the 1920s.
1909 – Seattle: The landscaping (by the Olmsted brothers) from the Alaska–Yukon–Pacific Exposition (AYPE) in Seattle still forms much of the University of Washington campus. The only major building left from the AYPE, Architecture Hall, is used by the university's architecture school.
1915 – San Francisco: The Palace of Fine Arts in San Francisco and its adjacent artificial lagoon are the only major remnants of the Panama–Pacific International Exposition still in their original locations on the former fairgrounds (now the city's Marina District neighborhood), but the building is almost entirely a reconstruction. The plaster-surfaced original, not intended to survive after the fair, was a crumbling ruin in 1964 when all but the steel framework was demolished so that it could be reproduced in concrete. The San Francisco Civic Auditorium, now the Bill Graham Civic Auditorium, is another major legacy of the fair but was built off-site in the city's Civic Center. The independent Panama–California Exposition in San Diego left a substantial legacy of permanent buildings and other structures which today define its site, San Diego's central Balboa Park, including the Prado walkway, the California Tower and Dome (now home to the Museum of Us), the 1,500-foot Cabrillo Bridge, the lily pond and botanical gardens, and the Spreckels Organ Pavilion.
1929 – Seville and Barcelona: much survives from the two simultaneous fairs Spain hosted that year. The most famous are the remnants of the Ibero-American Exposition in Seville, in which the Spanish Pavilion's Plaza de España forms part of a large park and forecourt. Most of that fair's pavilions have survived and been adapted for other uses, with many of them becoming consulates-general for the countries that built them. The Barcelona International Exposition featured the famous German pavilion designed by Mies van der Rohe, which was demolished but later rebuilt on the original site.
1936 – Johannesburg: The Empire Exhibition, South Africa was built close to the University of the Witwatersrand, and by the late 1970s the growth of the university was large enough to incorporate the permanent buildings from the exhibition. In 1985, the university purchased the South African Government Building; the two Heavy Machinery Halls, now called Empire Hall and the Dining Hall; the Hall of Transport; the Tower of Light; the Cape Dutch complex; and the Bien Donne Restaurant.
1942 – Rome: A special case is the EUR quarter in Rome, built for a World's Fair planned for 1942 but cancelled because of World War II. Today it hosts governmental and private offices, and several museums.
1958 – Brussels: In Brussels, the Atomium still stands at the exposition site. It is a 165-billion-times-enlarged iron-crystal-shaped building. Until June 2012, the "American Theatre" on the Expo grounds was frequently used as a television studio by the VRT.
