Stairs and (more recently) elevators are used to access the upper-level walkways in the buildings. Counterweights and hydraulics are located at the foot of each tower and are used to open the highway, which is still done on a regular basis to allow ships to pass. The weight of the bridge itself is so slight in comparison that it does not affect the operation of the structure. The base of the central tower has three floors: an exhibition space called "The Engine Room" which covers about, two large basement levels containing machinery and water storage tanks for the counterweights at the top of the tower. The first floor consists of a single walkway wide with parapets on both sides; this level is accessible by elevator from the second floor. There are shops on one side and offices on the other. The highest level is the roof where there are restaurants and bars. Only the central tower of the pair rises more than. The other is slightly shorter but wider, being instead of. It was built as a replacement for the original 1849 bridge that collapsed due to neglect. The new bridge was designed by Sir John Wolfe-Bennett, who also designed the Eiffel Tower. It was opened on May 23, 1890, just four months after its sister bridge.