The Alter Elbtunnel (also Old Elbe Tunnel, St. Pauli Elbe Tunnel) is a pedestrian, bike and motorist tunnel, which travels underneath the River Elbe and connects central Hamburg to the southern side of the river. While walking, be sure to look at the artworks that line the tiled walls. Travelers enjoyed the experience of walking beneath the river and taking in the great view from the opposing side. Free of charge for pedestrians and bikers, motorists are charged a small fee. You'll find the Elbe Tunnel open 24 hours a day (for pedrestrians/bikers) off the Landungsbrücken U-bahn stop.

• Go out and back to the river to 'Aussichtspunkt Steinwerder' for great views on Landungsbrücken and the sights behind. … You find the tunnel at Landungsbrücken in the building having the biggest green dome. Signs to 'Aussichtspunkt Steinwerder' also point to it." -- Wikitravel