Hyde Park Obelisk is an obelisk located in Hyde Park in Sydney, New South Wales, Australia. It sits at the intersection of Elizabeth Street and Bathurst Street. Unveiled in 1857 by the then Lord Mayor, George Thornton, it served as a sewerage educt vent to allow the escape of noxious gases from the sewer (although it now ventilates the stormwater system, following works to separate Sydney's sewerage and stormwater systems). The Hyde Park Obelisk was the first special sewer ventilation shaft built in Sydney and New South Wales, and is the only example of a sewer ventshaft constructed of sandstone within the Sydney Water system. It was modeled on Cleopatra's Needle on the banks of London's River Thames. The overall structure is 22 metres high, which comprises a square sandstone base 6.5 metres high.