Half-timbered townhouses frame the Altstadt’s main plaza Am Markt, a much-loved student hang-out. Rising above it is the 15th-century Rathaus , with a riotous baroque facade and an astronomical clock. Statues of four women representing the seasons grace the Neptunbrunnen opposite. Keep an eye out for No 15 , where a white window frame identifies a secret room where Jews hid in WWII.