Dreikönigenpförtchen is a small Gothic gate tucked into Cologne's old town, once leading into an immunity attached to the convent at St. Maria im Kapitol. It is easy to miss, but its pointed arch and compact stonework make it a rewarding detail for slow walkers.
Do not cross town for it alone. See it while visiting St. Maria im Kapitol or the nearby Romanesque churches, when the gate adds one more piece to Cologne's dense medieval street history.