In the basement of Paramount Apartments, 30 William Street, is a dark underground secret. When William Street was no more than a muddy horse track in the 1820s, its gradient and topography were very different and much steeper.

Just east of today’s Museum site was a small stream and bridge over the dip, before the track made a steep ascent up to where Kings Cross now is.
Over this creek was a substantial stone bridge, built in 1837.

In the dark basement of 30 William Street behind its modern louvered glass façade lies the northern part of the original stone bridge, designed by Town Surveyor, Felton Mathew. The bridge was built by Thomas Brodie in 1837.

These bridge remnants are some of the oldest surviving bridge remnants on mainland Australia and area a heritage item. They are the only known surviving example of a stone bridge within or near the township boundaries of Sydney prior to 1850 still in existence.

Later a sewer was built under the bridge in 1864-1867. It also still lies under the building and continues to operate today.