10 most difficult build­ings riddles

The Roman Theatre of Orange, France was built in the early 1st century. It is one of the best preserved of all Roman theatres and is currently used as a festival site called Chorégies d'Orange. In 1981, UNESCO declared the theatre as a World Heritage Site.

Washington Union Station is a major train station, transportation hub, and leisure destination in Washington, D.C. Opened in 1907, it is Amtrak's headquarters and the railroad's second-busiest station with annual ridership of just under 5 million and the ninth-busiest in overall passengers served in the United States. Daniel Burnham, a famed Chicago architect wrote; "The station and its surroundings should be treated in a monumental manner, as they will become the vestibule of the city of Washington, and as they will be in close proximity to the Capitol itself."

Argentina maintains the most permanent polar stations - 6, Chile - 5, Russia - 5.

Hohokam culture, prehistoric North American Indians who lived approximately from 200 to 1400 ce in the semiarid region of present-day central and southern Arizona, largely along the Gila and Salt rivers. The term Hohokam is said to be Pima for “those who have vanished.”

Mysore is commonly described as the "City of Palaces", and there are seven palaces including this one. The current structure was constructed between 1897 and 1912, after the Old Palace was burnt ablaze. Ambavilas Palace is one of the most famous tourist attractions in India, after the Taj Mahal, with more than 6 million annual visitors.

The unfinished obelisk in Aswan, Egypt is nearly one-third larger than any ancient Egyptian obelisk ever erected. If finished it would have measured around 42 m and would have weighed nearly 1,090 tons.

Le Corbusier was one of the most influential and controversial artists of the 20th century, and the pioneer of what is now called modern architecture. His five-decade career reshaped cities from South America to India. In 2016, seventeen of Le Corbusier's buildings, spanning over seven countries, were inscribed to the UNESCO World Heritage Sites list.

Designed by the French structural engineer Michel Virlogeux and British architect Norman Foster, it is the tallest bridge in the world. The P2 pier of the Viaduct is 343.0 meters (1,125 ft) tall, 19 meters taller than the Eiffel tower.

In the years of splendor in Venice there was a law that allowed only one building to wear the name of the palace - it was the Doge's Palace, the residence of the rulers of Venice. The rich Venetian families lived according to this law in the so-called houses (Casa abbreviated Ca). Currently, most residences of Venetian patricians carry the word "palace" in their name, although there are exceptions and some Venetian monuments are still called according to old traditions, eg Ca'Rezzonico or Ca 'd'Oro. Over 100 survived to modern times.

Las Lajas Sanctuary is a basilica church located in the southern Colombian, and built inside the canyon of the Guáitara River. The present church was built in Gothic Revival style between 1916 and 1949. The name Laja comes from the name of a type of flat sedimentary rock similar to shale and slate.It rises 100 metres high from the bottom of the canyon and is connected to the opposite side of the canyon by a 50 metres tall bridge.