Work to transform Inverness Castle into a tourist attraction is expected to start later this year.
Built on a hill overlooking the River Ness, the property is currently the base for the city's courts service.
But the Scottish Courts and Tribunal Service is preparing to vacate the castle and move into a new building.
Highland Council is leading the project to create a museum, art galleries and hotel accommodation at the site.
A contract for work including asbestos and timber preservation surveys and structural checks will be put out to tender in May.
Planning applications for hoardings to screen the castle during construction phases, and to change the use of the building, are expected to be submitted between March and June.
The castle could open as an attraction 2025, depending on what is identified in the surveys and structural checks.
The project forms part of the £315m Inverness and Highland City-Region Deal, which involves investment from the Scottish and UK governments, Highland Council, Highlands and Islands Enterprise and University of the Highlands and Islands.
Inverness and area provost Helen Carmichael said the castle project was "vital" to the regeneration of Inverness city centre, and the wider tourism economy of the Highland region.
She said: "I am excited at the future prospects of Inverness Castle becoming a 'must-see' attraction that will draw visitors to the Highlands."
Rural Economy and Tourism Secretary Fergus Ewing added: "We want to see a new life for the castle that builds on its existing attraction, offering visitors and locals alike a quality offering that encourages tourists to both visit and stay longer in the area."
The sandstone castle was built in 1836.
It was constructed on a mound overlooking the city and the River Ness. In 1848, a building known as the North Block was added and served as a prison.
It is thought that there may have been a castle on the site from as far back as the 11th Century.