Gillespies created a landscaped courtyard as part of an extension for the British Museum in London designed by world-famous architecture practice Rogers Stirk Harbour + Partners.
The courtyard provides a distinctive, yet naturalistic setting where visitors can retreat from the bustle of city life. The extension, called the World Conservation and Exhibitions Centre, cost £135 million and is one of the largest redevelopment projects in the British Museum's 260-year history.
It is one of six projects shortlisted for the award. Other entries include Hastings Pier by drMM Architects and Barrett’s Grove, Stoke Newington, by Groupwork and Amin Taha.
The winner will be announced by the Royal Institute of British Architects (RIBA) on 31 October at the Roundhouse in London.
The prize for excellence in design is named after the architect James Stirling and awarded annually by the RIBA. Past winners have included Zaha Hadid and Herzog & de Meuron.