James Barnet, occupies a prominent headland location and retains much of its layout and form. It may be significant at a state level as part of a suite of harbour fortifications. The place has a strong or special association with a person, or group of persons, of importance of cultural or natural history of New South Wales's history. The state heritage significance of the former Greycliffe Estate, now known as Nielsen Park, may be enhanced through its strong associations with important figures in the history and development of NSW. It is associated with John and Fanny Reeve, the Wentworth family (in particular Fitzwilliam Wentworth) and a range of notable tenants who were prominent men and women from the political, legal and commercial circles of 19th century Sydney. Also associated with this period of the site's development is noted mid-19th-century architect and surveyor, John F. Hilly who designed Greycliffe House and its outbuildings. The use of Greycliffe as an Infant Hospital saw a close association with eminent paediatrician Dr Margaret Harper, whose work on infant diet, care and disease has remained highly influential. Nielsen Park has a strong association with William Notting, Secretary of the Harbour Foreshores Vigilance Committee and Park Trustee, who led the public move to have the area preserved. The name of the reserve, Nielsen Park, acknowledges the Secretary of Lands at the time, Niels Nielsen who provided government support for the establishment of the park. Some buildings related to the 20th-century use of the site as a public place of leisure, such as the Dressing Pavilion, are associated with the Unemployment Relief Work Fund which employed builders during the Great Depression. The place is important in demonstrating aesthetic characteristics and/or a high degree of creative or technical achievement in New South Wales. Nielsen Park may be of state heritage significance as it contains two fine architectural examples of mid-19th-century residential buildings. Greycliffe House and its related outbuildings designed by architect J F. Hilly; and the Steele Point Battery and Barracks and associated cottage designed by Colonial Architect, James Barnet. The buildings are still situated in their landscape setting. In addition, a diverse range of recreational park buildings such as the kiosk, cottage, dressing shed and toilet buildings (mostly from the office of the Government Architect) are also extant and in their landscape setting. They all are excellent examples of their type and demonstrate the importance of the