A new observation deck that lets members of the public view the internal machinery of Victoria's newest bridge will open to the public tomorrow.

The City of Victoria says the new bascule pier observation deck on the Johnson Street Bridge also provides unique views of the upper and lower inner harbours.

A southside pedestrian-only walkway, interim public plaza spaces and sidewalk connections will also open tomorrow.

The $105-million Johnson Street Bridge opened to traffic in March after several years of delays and cost overruns.