People take photos with the skyline of the central business district in Singapore on September 10, 2015. (Photo by Edgar Su/Reuters)

The launch of a rocket into space is projected on Dubai's Burj Khalifa on February 9, 2021 as the UAE's “Al-Amal” – Arabic for “Hope” – probe's to Mars carries out a tricky manoeuvre to enter the Red Planet's orbit. A tense half-hour today will determine the fate of “Hope”. If successful, the probe which is designed to reveal the secrets of Martian weather, will become the first of three spacecraft to arrive at the Red Planet this month. (Photo by Giuseppe Cacace/AFP Photo)

A fado singer smokes a cigarrette outside a fado house at the Alfama neighborhood in Lisbon on May 8, 2019. From fado sounds to Cape Verde mornas or bossa nova: the Lisbon nights, where musicians from all over the world meet, have largely inspired Madonna's new album, who has been in the Portuguese capital since 2017. (Photo by Patrícia de Melo Moreira/AFP Photo)

The buildings of the banking district are seen through thousands of rain drops on a glass railing in central Frankfurt, Germany, Wednesday, January 11, 2017. (Photo by Michael Probst/AP Photo)

Commuters by with the buildings of the banking district in background in Frankfurt, Germany, Thursday, February 6, 2020. (Photo by Michael Probst/AP Photo)

These are the ambitious plans which suggest skyscrapers of the future may house an entire city. The Endless City project is an award-winning proposal by sure Architecture, who propose turning skyscrapers into complete ecosystems. London is the proposed city for the mixed-use tower – which would feature huge ramps linking different sections of the structure. The company, whose design won the SkyScrapers and SuperSkyScrapers Competition, insist the structure would be a great space-saver in dense cities which have previously spread outwards rather than upwards. (Photo by Caters News)

A man sleeps between tombstones in front of his single-room home on a hot night in the Cairo Necropolis, Egypt, October 13, 2015. In the sprawling Cairo Necropolis, known as the City of the Dead, life and death are side by side. Amid a housing crisis in Egypt, and with the population of greater Cairo estimated at about 20 million, people count themselves lucky to have a place to call home in the graveyards that date back hundreds of years. (Photo by Asmaa Waguih/Reuters)

Kale grows at Kajodlingen farm in Gothenburg, Sweden, September 28, 2016. They are doing it on the rooftops, on tower block balconies and even on a disused railway: Swedes have discovered a passion for urban gardening as a way of growing fresh food and getting back in touch with nature. Part of a global movement, an increasing number of Swedish city-dwellers are growing their own in window boxes and allotments or are visiting public gardens built in or on industrial or office spaces. (Photo by Maxim Shemetov/Reuters)