The Hyde Park Obelisk is a heritage-listed obelisk that served as a sewer vent and is now a monument located in Hyde Park at the intersection of Elizabeth Street and Bathurst Street, in the Sydney central business district, in the City of Sydney local government area of New South Wales, Australia.

[1] Completed in the Victorian Egyptian style, it was modelled on Cleopatra's Needle on the banks of London's River Thames.

The shape of the cowling on the older types of vents were set to produce either eduction or induction whenever there is a natural breeze.

[4] On 7 November 2014, the Hyde Park Obelisk was covered with a giant pink condom as a temporary installation to raise awareness about HIV, primarily in Sydney's LGBTIQ community.

[5][6] Completed in 1857, the obelisk is a simple masonry shaft consisting of a sandstone base and decorative bronze ventilator apex.

The only means of ventilating this system was a sandstone ventshaft, which was erected at Hyde Park (corner of Bathurst and Elizabeth St) in 1857.

[1] Of the methods investigated and adopted, including street vents, house vents (cast iron traps and water traps) and flues, the tall ventshafts were determined by J. M. Smails in several reports to the government of the day, to be the most efficient way of dispersing the pressure and gases found within the sewers.

[1] Initially, after the Obelisk, ventshafts were constructed using bricks, were ornate and fairly major features in the city landscape.

[1] Sewer Vent was listed on the New South Wales State Heritage Register on 15 November 2002 having satisfied the following criteria.

[1] The place is important in demonstrating aesthetic characteristics and/or a high degree of creative or technical achievement in New South Wales.

The Obelisk is a sandstone vent shaft which displays the classical architecture and technology of the late nineteenth century.