More than 900 walkers are due to set off from Lochaber tomorrow morning on a gruelling 54-mile trek that it is hoped will raise around £500,000 for charity.
In less than 24 hours, they will walk the equivalent of two marathons and climb the height of Ben Nevis twice while taking part in the annual Caledonian Challenge.
Around 200 teams of at least four people will leave Gairlochy at hourly intervals from 7am on the route, which follows the south end of the Great Glen Way.
Walkers then trek through the night, passing Kinlochleven and Glencoe, continuing along the West Highland Way before reaching Tyndrum.
More than £12.5million has been raised in over 15 years since the event began.
All the money has been donated to Foundation Scotland – formerly the Scottish Community Foundation – directly benefiting small charities and community groups across Scotland.
Erin Byrne, who is spokeswoman for the foundation’s events team, could not say how much this year’s event would raise at this stage.
She said: “Last year, it raised more than £500,000 and we’re hoping to achieve that figure again this year.
“It’s impossible to say how much we will raise until all the donations come in and that can take up to several weeks after the event.”
Miss Byrne added that they stagger the start time so those who might take a bit longer to complete the course can start earlier.
And they are hoping the weather will be kind to them this weekend.
She said: “The forecast is looking good at the moment, with quite a sunny day on Saturday, so we’re fairly optimistic for a dry weekend.”
Another 100 walkers will be taking part in the 24-mile Caledonian Hike from Fort William to Glencoe tomorrow.
The challenge takes an average of 22 hours to complete and the average time for the hike is 10 hours.
Since 1997, more than 16,000 walkers have taken part in the challenge.
It is estimated that, on average, they take 130,000 steps along the 54-mile route and drink around 15 litres of water.