A concept illustration of the world's first forest in the sky, the Bosco Verticale green twin towers currently under construction in Milan, Italy. Towering over the city skyline the world's first forest in the sky will be a sight to behold. With tree equal to one hectare of forest spanning 27 floors these 365 and 260 foot emerald twin towers will be home to an astonishing 730 trees, 5,000 shrubs and 11,000 ground cover plants. (Photo by Boeri Studio)

The Mano de Desierto is a large-scale sculpture of a hand located in the Atacama Desert in Chile, 75 km to the south of the city of Antofagasta, on the Panamerican Highway. The nearest point of reference is the “Ciudad Empresarial La Negra” (La Negra Business City). The sculpture was constructed by the Chilean sculptor Mario Irarrázabal at an altitude of 1,100 meters above sea level. Irarrázabal used the human figure to express emotions like injustice, loneliness, sorrow and torture. Its exaggerated size is said to emphasize human vulnerability and helplessness. The work has a base of iron and cement, and stands 11 metres (36 ft) tall. Funded by Corporación Pro Antofagasta, a local booster organization, the sculpture was inaugurated on March 28, 1992.

During the feudal times, the society was very structured where everyone knew their place. Fishermen knew that they would always have to bend their knee for highborn ladies and gentlemen, while the latter considered themselves to be far too superior to even look at the common folk. Mont Saint-Michel is a living memorial of those times. Its structural composition clearly reflects the structure of feudal society: The monastery and abbey were built on the highest point; housing and stores were built some distance below; finally, fishermen’s and farmer’s houses were constructed, not even being within the city walls, making them the most vulnerable to the possible attack.

In this Wednesday, March 18, 2015 photo, limestone quarry workers walk through a cloud of dust spewed into the air by rotor blades of the stone-cutting machinery in the desert of Minya, southern Egypt. Around 45,000 people, including children, work in an estimated 1,500 quarries, digging out stones that later will be used in construction or powdered to be used by pharmaceutical and ceramic companies. (Photo by Mosa'ab Elshamy/AP Photo)

Central Bangkok and the Chao Phraya River are seen from an abandoned skyscraper in Bangkok April 19, 2015. The abandoned building, known as Satorn Unique, dubbed the “ghost tower” was destined to become one of Bangkok's most luxurious residential addresses but construction was never completed as the Thai economy was hit during the 1997 Asian Financial Crisis. Now, many travellers visit and explore 49-storey skyscraper. (Photo by Athit Perawongmetha/Reuters)

Artists perform during the opening show directed by German director Volker Hesse, on the opening day of the Gotthard rail tunnel, at the fairground Rynaecht at the northern portal in Erstfeld, Switzerland, Wednesday, June 1, 2016. The construction of the 57 kilometer long tunnel began in 1999, the breakthrough was in 2010. After the official opening on June 1, the commercial operation will start in December 2016. (Photo by Ruben Sprich\Pool Photo via AP Photo)

Rescuers search for survivors in the rubble of a collapsed residential building in Makongeni estate in Nairobi December 17, 2014. Three more bodies were recovered on Wednesday night from the building that collapsed in Makongeni estate in Nairobi, raising the death toll to four, Kenya Red Cross has reported. The residential building whose sixth floor was still under construction had allegedly not been cleared for occupation by the Nairobi City County and its owner has been missing since it collapsed. A search and rescue and rescue operation is ongoing for the unknown number of people still trapped under the rubble, Kenya Red Cross also reported. (Photo by Thomas Mukoya/Reuters)

The Haʻikū Stairs, also known as the Stairway to Heaven or Haʻikū Ladder, is a steep hiking trail on the island of Oʻahu. The trail began as a wooden ladder spiked to the cliff on the south side of the Haʻikū Valley. It was installed in 1942 to enable antenna cables to be strung from one side of the cliffs above Haʻikū Valley to the other. A building to provide a continuous communication link between Wahiawā and Haʻikū Valley Naval Radio Station was constructed at the peak of Puʻukeahiakahoe, elevation about 2,800 feet (850 m). The antennae transmitted very low frequency radio signals from a 200,000-watt Alexanderson alternator in the center of Haʻikū valley. The signals could reach US Navy submarines as far away as Tokyo Bay while the submarines were submerged.