The Bridge of Sighs (you can only see the bottom part of it in the foreground) is made of white limestone and has windows with stone bars. It passes over the Rio di Palazzo and connects the New Prison to the interrogation rooms in the Doge's Palace.
The view from the Bridge of Sighs was the last view of Venice that convicts saw before their imprisonment. The bridge name, given by Lord Byron in the 19th century, comes from the suggestion that prisoners would sigh at their final view of beautiful Venice through the window before being taken down to their cells. In reality, the days of inquisitions and summary executions were over by the time the bridge was built and the cells under the palace roof were occupied mostly by small-time criminals.
A local legend says that lovers will be granted eternal love and bliss if they kiss on a gondola at sunset under the Bridge Of Sighs.(wikipedia)