Helsinki-to-Tallinn Tunnel

The Helsinki–Tallinn Tunnel (also known as FinEst or Talsinki tunnel) is a proposed undersea tunnel that would span the Gulf of Finland and connect the Finnish and Estonian capitals by train. The tunnel's length would depend on the route taken: the shortest distance across would have a submarine length of 80 km (50 mi), which would make it 40% longer than the current longest railway tunnel in the world, the 57 km (35 mi)-long Gotthard Base Tunnel in Switzerland. During the 2010s, it was estimated that the tunnel, if constructed, would cost €9–13 billion and could open in the 2030s if approved. In 2013, the European Union approved €3.1 million in funding for feasibility studies. A 2015 pre-feasibility study proposed trains traveling with a top speed of 250 km/h (155 mph).

Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).