The Eysturoyartunnilin tunnel system under the North Atlantic Ocean facilitates travel time between the islands of the Faroe Islands in Denmark.
Eysturoyartunnilin Tunnel: World's First Undersea Roundabout
After 3 years, the Eysturoyartunnilin tunnel was opened in 2020, costing $166 million. Designed by engineer Tronsdur Patursson resembling a jellyfish, it is the largest infrastructure investment ever undertaken in the Faroe Islands.

The 11km-long Eysturoyartunnilin Tunnel reduces travel time from the capital Torshavn to Runavik from 1 hour 14 minutes to just 16 minutes. Its deepest point is 187 meters below sea level. To ensure safety, the contractor had to ensure that the steepest gradient did not exceed 5%. The central area features sculptures and a lighting system.

All vehicles passing through the Eysturoyartunnilin tunnel must pay a fee. Local residents can opt for package deals to save costs. With this project, 90% of the island's population can travel more easily between the islands.

The Faroe Islands are a chain of 18 islands in the North Atlantic Ocean. Construction of tunnels through the steep mountains on the islands began in the 1960s. Today, the archipelago boasts 19 tunnels.
As per Monster
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Reference: Mytour's travel handbook
MytourJune 25, 2021