The E10 crosses the Nappstraumen strait in Lofoten through an undersea tunnel of 1.8 kilometres. It binds Flakstadøya to the rest of the island chain.

The tunnel opened on 11 July 1990 and replaced the ferry crossing between Lilleeidet and Napp, which had run since 1956. It reaches 63 metres below sea level, and the steepest gradient is 8 percent.

The tunnel is being upgraded to meet today's safety requirements, and the work is expected to finish in 2027. It is closed at night for the whole period, and by day traffic passes in convoy behind a lead vehicle. That makes this particular status extra useful: check it before you drive, especially at night.