Hoskins Architects will design a new Rosewood hotel at Edinburgh's former Royal High School, a historic landmark building on Calton Hill in the centre of the Scottish capital that has stood vacant for almost 50 years.

The neoclassical, listed building was originally designed by architect Thomas Hamilton and completed in 1829. The plan to invest more than £75m ($115m, €102m) to restore and convert the property is led by Duddingston House Properties and Urbanist Hotels.

The 147-bedroom hotel will include a Sense spa, fitness centre, indoor swimming pool, three restaurants and bars, and a 3,200sq ft (297sq m) ballroom.

Gareth Hoskins, the architect for the project, said the new designs respond to comments made by heritage organisations and the public.

“The design focuses around an informed restoration of the central Hamilton-designed building, repairing its decaying fabric and maintaining the strong sculptural presence of its frontage without intervention,” said Hoskins.

The existing Greek revival building will house the public areas of the hotel, allowing its spaces to be fully accessible to the public for the first time in the building's history. The hotel’s bedrooms will be set away from the original building in two newly constructed wings.

“Their organic shape, with landed terraces and undulating copper facade, inspired by the layered volcanic landscape of both Calton Hill and nearby Salisbury Crags, allow the new wings to blend with the surrounding hill,” said Hoskins. “The contrast of the form and colour of the new elements, together with the considered approach to the landscaping of not just the site, but the streetscape around the former high school, allow this hugely important building to retain and reinforce its prominence as a key Edinburgh landmark.”

Rosewood is experienced in restoring and transforming historic buildings; it is overseeing the restoration of the iconic Hotel de Crillon in Paris, and also recently announced it will transform a landmark Brazilian hospital into a hotel and spa.

“The former Royal High School is one of Edinburgh’s most important landmarks, and we will be drawing on our experience with historic properties such as The Carlyle, Rosewood Castiglion de Bosco and Hotel de Crillon, to ensure the heritage and history of this building is preserved and celebrated,” said Radha Arora, president of Rosewood Hotels & Resorts.

Independent research from Oxford Economics has estimated that the hotel could contribute £31.5m ($48m, €42.3m)to Edinburgh’s GDP and £36.7m ($56m, €50m) to Scotland’s economy on an annual basis.

Hoskins was also responsible for the redevelopment of the National Museum of Scotland, and will be designing the extension for the National Galleries of Scotland.