The Netherlands' first road tunnel under a river, connecting the north and south banks of the Nieuwe Maas. Built in the late 1930s, it is notable not for its engineering (though that was impressive for the time) but for its interiors: the entrance halls are pure Art Deco, with geometric tilework, elegant lighting fixtures, and a streamlined aesthetic that makes descending into a car tunnel feel oddly glamorous.
The pedestrian and bicycle tunnel runs parallel to the car tunnel and is the best way to experience it — ride or walk through the tiled tube, admire the curved walls, and emerge on the south bank near the old Katendrecht neighbourhood. Free to use at any time. The entrance buildings on both banks are worth a look in their own right.