Great Wall of China: The 4,160-mile barricade running from east to west is the world's longest man-made structure. The fortification was built to protect various dynasties from invasion by Huns, Mongols, Turks and other nomadic tribes. Construction took place over hundreds of years, beginning in the seventh century B.C.

Hagia Sophia, Turkey: The soaring cathedral, also called the Church of Holy Wisdom, was built in 537 B.C. at Constantinople, today's Istanbul. In 1453, when Constantinople fell to the Ottomans, it became a mosque with minarets. When Turkish President Kemal Ataturk turned it into a museum in 1935, Christian mosaics covered up by the Muslims were revealed.

Kiyomizu Temple, Japan: Kyoto's Kiyomizu-dera, which means Clear Water Temple, was founded by a Buddhist sect in 798 and rebuilt in 1633 after a fire. Drinking from its three-stream waterfall is believed to confer health, longevity and success.

Kremlin and St. Basil's Cathedral, Russia: Onion domes with golden cupolas surrounded by red brick walls are at the heart of Moscow's Kremlin, a Medieval fortress converted into the center of Russian government. The Kremlin once symbolized Soviet communism. The Cathedral of St. Basil the Blessed on adjacent Red Square features nine towers of different colors. It was built by Czar Ivan the Terrible in the mid-16th century.

Machu Picchu, Peru: Built by the Incan Empire in the 15th century, Machu Picchu's walls, palaces, temples and dwellings are perched in the clouds at 8,000 feet above sea level in the Andes overlooking a lush valley 310 miles from Lima.

Neuschwanstein Castle, Germany: The inspiration for the Sleeping Beauty Castle at Disneyland, Neuschwanstein is a creation of "Mad King" Ludwig II of Bavaria, who had it built in the 19th century to indulge his romantic fancies. Perched on a peak in the Bavarian Alps, the gray granite castle rises to towers, turrets and pinnacles and contains many paintings with scenes from Richard Wagner operas admired by Ludwig.

Petra, Jordan: This ancient city in southwestern Jordan, built on a terrace around the Wadi Musa or Valley of Moses, was the capital of the Arab kingdom of the Nabateans, a center of caravan trade, and continued to flourish under Roman rule after the Nabateans' defeat in A.D. 106. The city is famous for water tunnels and stone structures carved in the rock, including Ad-Dayr, "the Monastery," an uncompleted tomb facade that served as a church during Byzantine times.

Pyramid at Chichen Itza, Mexico: This step pyramid surmounted by a temple was part of a sacred site in an important Mayan center on Mexico's Yucatan peninsula. It is built according to the solar calendar. Shadows at the fall and spring equinoxes are said to look like a snake crawling down the steps, similar to the carved serpent at the top. An older pyramid inside features a jade-studded, red jaguar throne.

Pyramid of Giza, Egypt: The only surviving structures of the original seven wonders, the three pyramids were built as tombs for pharaohs 4,500 years ago. Nearby is the Great Sphinx statue, with a man's face and a lion's body.

Statue of Liberty, New York: The 305-foot statue in New York Harbor has welcomed immigrants and symbolized freedom since 1886, when it was dedicated as a gift of the French government.

Stonehenge, Britain: How and why this circular monument of massive rocks was created between 3,000 and 1,600 B.C. is unknown, but some experts say the stones were aligned as part of a sun-worshipping culture or astronomical calendar. Today it is a major tourist attraction. Druids and New Age followers gather here every June 21 to celebrate summer solstice.

Sydney Opera House, Australia: Situated on Bennelong Point reaching into Sydney's harbor, the opera house was designed by Danish architect Jorn Utzon and opened in 1973 by Queen Elizabeth II. Its roof resembles a ship in full sail and is covered by over 1 million white tiles. The building has 1,000 rooms.

Taj Mahal, India: The white marble-domed mausoleum in Agra was built by a 17th century Mogul emperor for his favorite wife, who died in childbirth. The architecture combines Indian, Persian, and Islamic styles. The complex houses the graves of the emperor, his wife, and other royalty.

Timbuktu, Mali: Two of West Africa's oldest mosques, the Djingareyber, or Great Mosque, and the Sankore mosque built during the 14th and early 15th centuries can still be seen here in the northern Sahara Desert. Founded about A.D. 1,100, Timbuktu was a flourishing caravan center in the Arabic world and a leading spiritual and intellectual center in the 15th and 16th centuries, with one of the world's first universities.