India's 100th airport is arguably one of the world's most beautiful airports.

India's 100th airport, which was inaugurated by Prime Minister Narendra Modi in the northern-eastern state of Sikkim on Monday, is arguably one of the world's most beautiful airports.

The state's airport at Pakyong, some 30km (18 miles) from the state capital, Gangtok, and has been described as an "engineering marvel". Some 60km from the border with China, the airport is located on top of a hill above Pakyong village at 4,500ft (1,371 metres) above sea level and it's spread across over 201 acres.The airport is flanked by deep valleys at both ends of the 1.75km-long runway. It has two parking bays and a terminal building, which can handle about 100 passengers at a time.Difficult topography and hostile weather conditions made this nine-year-long project "extremely challenging and exciting", according to a spokesperson for Punj Lloyd, an Indian company which built the runway. Engineers say the main challenge was to carry out heavy earthwork construction at the site and lug equipment through narrow mountain roads. The weather -- Sikkim gets monsoon rains from April to September -- hindered work. The hilly terrain and high seismicity were among some of the other challenges engineers faced on the rocky slopes.

The entire airport, including the runway, has been built on land which was itself created by building an embankment wall as high as 263ft in deep valleys. Punj Lloyd says it is one of the tallest "reinforcement" walls in the world. Commercial flight operations from Pakyong will begin on 4 October. The airport is expected to boost tourism to Sikkim, which is home to a number of peaks, glaciers and high altitude lakes