The trust which owns Ben Nevis believes a musical instrument buried in a stone cairn on the summit was carried there by a gang of Dundee removal men.
Kenny Campbell intended to retrieve the instrument
The John Muir Trust said a sell-by date on a biscuit wrapper found with the remains matches the period of the Dundonians' charity stunt in 1986.
Former Highland Games athlete Kenny Campbell thought it was an organ he carried to the peak 15 years earlier.
The trust said the removal men would not be hit with a litter fine.
Volunteers who were reducing the number of cairns on the mountain, near Fort William, found the frame of a keyboard instrument.
Mr Campbell, 64, from Ardgay, believed it was an organ he lifted to the summit in 1971.
However, the trust is certain it was a piano carried by 24 removal men 20 years ago.
One of the men from Dundee, Mike Clark, said they did it to raise money for charity.
He said: "We got up to the summit plateau but it was covered in mist and was very cold. So we sat down and drank a bottle of whisky and ate a packet of McVities biscuits.
"We decided it was best to break up the piano and carry it down in pieces, but we couldn't smash up the cast iron frame and the wooden casing attached to it.
"It was very cold touching the iron frame so we built a cairn of rocks around it and left it there. The biscuit wrapper blew into the cairn and was covered up too.
"We carried the keyboard down the mountain and the keys were given to everyone who took part as a memento of the trip."
Nigel Hawkins, director of the John Muir Trust, said the musical mystery had gained worldwide attention.
He added: "There is absolutely no question of a litter fine and the guys needn't worry about that.
"We are delighted to have solved the mystery of the piano on Ben Nevis.
"An organ was carried up by Kenneth Campbell in 1971, but we can say definitely that it was not an organ that was found as there was an iron frame with metal strings."