They had climbed, cycled and canoed across the breadth of Scotland, covering nearly 220km in a week - and they were still singing.
With a pound;12 guitar, 10 pupils from Banchory Academy in Aberdeenshire set off with their teachers on an incredible journey last summer.
With camping on the riverbank and cooking their meals on gas stoves, this was a week of survival without showers, hair-straighteners or flushing toilets.
The Across Scotland Challenge was completed on foot, mountain bike, raft and canoe. Only the last 16km were by powerboat - the final spurt up the River Tay from Perth to Broughty Ferry. It was like the finale in a Bond movie when the group's three powerboats bounced off the waves under the Tay Bridge.
But the trip, during school Activities Week, wasn't just about endurance and fitness. Each pupil collected sponsorship for The Archie Foundation, which raised almost pound;4,000 for Royal Aberdeen Children's Hospital.
The youngsters spent months planning the trip and trained for 16 weeks.
For the first few days, soaring temperatures proved too much for one pupil who became ill and had to go home. Then for the last few days it was the usual Scottish summer - snow on the Cairngorms and hail across northern Scotland.
Singing on the banks of the Tay while waiting for their powerboats, pupils and teachers looked as if they would sleep well at the end of it all. "These were long, long days," said PE teacher Lesley Bett, who travelled with them. "You've got to put everything into barrels for canoes, so if you do capsize, everything's dry. There was a lot of teamwork. Some of them just shone.
"There was no moaning or complaining - they just got on with it. They took to everything like ducks to water."
Team leader Colin Nicoll, a depute head and PE teacher, looked fit and happy to be on the final stage. "I was impressed with all of them," he said. "One girl is just a first year, one is second year and eight are third years. They're young for a trip like this and they've been great."
The youngest group member was Megan Ferguson. "I wanted to do something really different and I thought raising money for charity was a good thing to do," she said. "I really enjoyed the mountain-biking, the canoeing and going down the rapids."
The group mountain-biked for the first two days from Bridge of Awe, near Taynuilt, and headed into Glen Kinglass and stayed at a Glen Kinglass Lodge the first night.
"We cycled out through Glen Kinglass to join the West Highland Way and down to Tyndrum," Mr Nicoll said. "We walked on the West Highland Way, then cut off north and headed towards Glen Lochy and then we cycled from there down into Killin.
"Then we met the guys from Beyond Adventure, the company we used for the canoeing part of the trip and we had a short paddle that night out to Anthony's Island on Loch Tay."
Day Four was paddling the whole of Loch Tay - "probably the toughest day", said Mr Nicoll, because it was 22 miles into easterly winds. They then cycled eight or so miles from Kenmore to Aberfeldy and rafted from Aberfeldy through Grandtully to a campsite. The last two days they canoed along the Tay to Perth, camping by the riverside.
Headteacher Sheila Di Maio spent the first few days with the group, completing the 22-mile canoe journey on Loch Tay and later the final stretch on powerboats.
"I think they were most impressive - it was a very challenging trip both physically and mentally. They're a super group of kids and they never moaned once," she said.
Mr Nicoll added: "They had a fantastic journey and I saw several changes in them."
As they awaited the powerboats to head home, the pupils sang to accompaniment on their credit-crunch guitar, which had survived the rapids well. Star singer Chris Irvine (S3) said: "It's been really fun and very tiring. We are pretty shattered. I capsized in the canoe. We were going down the rapids and hit a rock side-on and flipped . This was the best trip we could have done."
Caitlin Soulsby (15), added: "It was tiring but really enjoyable. The rafting was good - and just completing it felt really good."
Her friend Helen Stirling thought: "Some of it was hard graft but it was fun." She was off home to sleep under her electric blanket.
Carol Brimble, a chemistry and support for learning teacher, also enjoyed their adventure.
"All of the activities were great and the pupils were fantastic," she said. "I would certainly do it again . definitely."
- Beyond Adventure, Aberfeldy.
T: 01887 829 202.