The Stadhuis is one of the very few buildings on the Coolsingel that survived the German bombing of 14 May 1940. Henri Evers's massive 1920 design — neo-Renaissance, with a 71-metre tower, ornate copper roofs, and a great cour d'honneur on the Coolsingel — sits in slightly absurd dignity among the postwar towers around it.
The interior is open for occasional guided tours and during Open Monument Days; the courtyard is freely accessible during office hours. Worth a circle even if you don't go in, just to see what Rotterdam's centre would have looked like otherwise.