Chennai-Rameswaram Route, India

A 2.06km-long sea bridge is part of the railway route that connects the city of Chennai to the pilgrimage town of Rameswaram on Pamban Island in south India. The Pamban Railway Bridge was built in 1914 over the Indian Ocean and is India's first cantilever bridge.

The central part of the bridge opens up to allow movement of ships and ferries. Though supported by 145 concrete piers, strong ocean currents and cyclones often pose a serious threat to both the bridge and train.

Aso Minami Route, Japan

Aso Minami Route, Japan's most dangerous railroad owing to its proximity to Mount Aso - the nation's biggest active volcano - passes through the region of Kumamoto, connecting Takamori to Tateno Station in Minamiaso.

The train tracks are next to the foothills of the volcano and visitors risk witnessing an eruption at any time. Hot lava is normally visible burning in the forest close to the tracks and visitors can watch steam rising from the volcano during fall.

Narizdel Diablo or Devil's Nose Train, Ecuador

Narizdel Diablo or Devil's Nose, a 12km stretch between Alausi and Sibambe in the Andes Mountains of Ecuador, was constructed around the Condor Puñuna or Condor's Nest mountain in 1902 as part of the Quito-Guayaquil railroad.

The Devil's Nose section is located 9,000ft above sea level and was considered one of the world's most difficult railways to engineer and construct. Travellers, although no longer allowed onto the roof of the train, can experience the steep climb up a series of switchbacks and a near-vertical drop of 500m.

Tren a las Nubes, Argentina

Tren a las Nubes or the 'Train to the Clouds', a train service passing through the Andes mountain range over a distance of 217km, connects Salta in north-west Argentina to La Polvorilla on the Chilean border. The railway line, opened in 1948 after nearly 27 years of construction, was originally constructed for socio-economic purpose but is now a tourist train departing from Salta on the 15-hour, 434km round-trip journey.

The zigzag railway route passes through 29 bridges, 21 tunnels and 13 viaducts including the Polvorilla viaduct. The viaduct is 224m-long and 13,845ft (4,220m) above sea level making it one of the world's highest railways.

White Pass and Yukon Route, Alaska, USA

The 110mi-long White Pass and Yukon Route, originally built during the Klondike Gold Rush to connect Skagway in Alaska and Whitehorse in Yukon Territory, Canada, was opened in 1900, but closed in 1982 following the collapse of the mining industry. It was, however, reopened in 1988 as a heritage railway for tourists to enjoy the steep gradients, cliff-hanging turns and scenic backdrop of mountains, glaciers and waterfalls.

The route climbs as high as 3,000ft in 20mi and includes two tunnels as well as the 110ft-long cantilevered Captain William Moore Bridge built in 1901.

Kuranda Scenic Railroad, Australia

The 34km Kuranda Scenic Railroad connecting Cairns to the town of Kuranda in Queensland, Australia, was constructed between 1882 and 1891 and passes through the dense tropical rainforest of the World Heritage-listed Barron Gorge National Park and the Macalister Range.

The tracks are built a few meters away from numerous waterfalls including the Barron Falls which spray the passengers with water. The railroad navigates through 15 tunnels, 93 curves and more than 40 bridges during the 1.45-hour one-way journey.

Georgetown Loop Railroad, Colorado, USA

Georgetown Loop is a heritage railroad that connects the neighbouring towns of Georgetown and Silver Plume in the Rocky Mountains of Colorado. The narrow gauge line was constructed in 1877 to provide access to silver mines and was closed in 1939 but reopened in 1984 to operate summer tourist trains.

The rail line spans 7.2km and runs along a 'corkscrew' route along the mountainous terrain, reaching an elevation of approximately 640ft. The route includes four bridges across Clear Creek Valley, including the 100ft-tall Devil's Gate High Bridge on which the train moves slowly and precariously.

Lynton & Lynmouth Cliff Railway, United Kingdom

The Lynton & Lynmouth Cliff Railway, an 862ft-long rail line spanning the English towns of Lynton and Lynmouth, starts from Lynmouth and glides up a 500ft-high steep cliff with a 58 percent gradient to reach Lynton.

The railway line began operational in 1890 and is situated in the centre of Exmoor National Park, offering spectacular views of Exmoor and the North Devon Coastline. Trains comprising two cars, each capable of carrying 40 people, operate on the route.

Cumbres and Toltec Scenic Railroad, New Mexico

Built in 1880, Cumbres and Toltec Scenic Railroad is a 64mi heritage railroad operating between Chama in New Mexico and Antonito in Colorado. The narrow gauge track was originally constructed as part of Rio Grande Railroad's San Juan Extension. The railroad has been carrying tourists through the scenic southern Rocky Mountains since 1971.

The route derives its name from the 800ft-high Toltec Gorge and the 10,015ft-high Cumbres Pass through which it passes. Cumbres Pass is the highest rail pass in the US. The steam-powered locomotive also negotiates through narrow ledges, a number of loops, trestles and tunnels to reach its destination.

Argo Gede Train Railroad, Indonesia

Argo Gede Train Railroad, a railway line in Indonesia between the capital city of Jakarta and Bandung, the capital of West Java province, passes through emerald green fields, lush mountains and deep river valleys.

The most dangerous stretch of the three-hour journey is the crossing of the Cikurutug Bridge. The train rides on the pylon trestle bridge 200ft above the valley floor, offering panoramic view of the subtropical valley below.