Helsinki’s tap water crawls for nine days through a 120-kilometre tunnel blasted into solid bedrock: One of the longest tunnels on Earth, hidden entirely underground

Residents across the Helsinki metropolitan area turn on their taps without seeing the extraordinary route their drinking water has taken. Before reaching homes, schools and businesses, the water spends about nine days flowing through the Päijänne Water Tunnel, a 120.3-kilometre passage carved deep into Finland’s granite bedrock.

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