Members of a mountain rescue team are to run and cycle the 96-mile (154km) West Highland Way to raise funds to buy new equipment.
Assynt MRT's challenge, on 20 December, will take place close to the shortest day of the year, meaning most of the activity will take place in darkness.
The Assynt rescue team's 30 members come from Caithness and Sutherland.
The team covers about 3,474 sq miles (9,000 sq km) of one of the most remote areas of Scotland.
Charlie MacLeod, from Assynt MRT, said: "To run and mountain bike almost 100 miles on rough terrain, in December, largely in the dark, you have to be a little mad."
He added: "The sheer size of our area, the scope of our responsibility and the relatively low population, present us with particular challenges.
"Not everyone realises that although we work under the auspices of the police we have to fund the majority of what we do ourselves.
"This includes everything from the upkeep of our rescue base and vehicles to purchasing equipment and providing first aid training."
Mr MacLeod along with team members Kirstin Caramouche, Dennis Gallagher, Tom Ross, Alan Sutherland, Doug Graham and Bob Kerr are expected to tackle the challenge.