In order to protect Rotterdam from floods, a storm-proof barrage was built on the Nieuwe Waterweg, between Maassluis and Hoek van Holland. Since May 1997, the Nieuwe Waterweg (360m wide) can be completely closed by two immense white metallic framed gates known as the two Leaning Eiffel towers beacuse of their shape. This completely automatic ensemble is unique in the world. A permanent exhibition on the barrage is in the Keringhuis information centre.