On Oudezijds Achterburgwal a distinctive gateway with spectacles over the pedestal rises up and marks the entrance to the Oudemanhuispoort, a 17th-century building that was once an almshouse for the elderly. You can't go inside the structure, as it's now part of the University of Amsterdam, but you can wander the leafy courtyard and secondhand book market that operates in the passageway.