The £2.2m appeal for a new cafe on top of Snowdon has received a major boost, as organisers travelled to the summit for a fundraising event.
Prince Charles called the café the 'highest slum in Wales'
A donation of several hundred thousand pounds was offered on Thursday to replace the mountain top cafe, famously labelled a "slum" by Prince Charles.
Until news of the donation, the appeal had managed to bring in just £20,000.
Organisers described the latest donation, from somewhere in the UK, as a "huge boost".
The news emerged as members of the appeal, accompanied by mountaineer and explorer Bear Grylls, were travelling up by the Snowdon Mountain Railway.
They were launching an international credit cards donation scheme designed to help meet the £2.2m appeal before the deadline next month.
The money is the last of £9.2m needed to replace the 70-year-old concrete structure.
It was built by Sir Clough Williams-Ellis, who also designed the Italianate village of Portmeirion a few miles away.
Aneurin Phillips, chief executive of the Snowdonia National Park Authority said that the donation could not have come at a better time.
He said the figure offered was more than £100,000 but less than £500,000 Appeal officials were now making further enquiries about the donor.
"If the money is not in place by the end of June, then our appeal will fail," said Mr Phillips, speaking on the summit.
"It will be a tragic loss if it does - 350,000 visitors come up Snowdon every year. They are met with classic views but a very unattractive building."
Mr Phillips agreed donations from the public had so far been "slow" but said in the last week they had been beginning to pick up. Donations from corporate sponsors were also being sought.
Previous attempts to redevelop the cafe once labelled the "highest slum in Britain" by Prince Charles fell by the wayside but last year authority planners approved a design.
The existing concrete building went up in 1935
It consisted of stone and glass building - designed to placate conservationists and blend in with the scenery.
The park authority and the Snowdon Society said they have already raised £7.2m of the money needed to replace the cafe and Snowdon Mountain Railway terminus.
The Welsh Assembly Government has pledged £3m and the appeal is also on course for £3.6m from Europe's Objective One regeneration funding scheme.
The Wales Tourist Board and Snowdon Mountain Railway have each pledged £200,000 or more. The park authority is making a similar contribution.
But Mr Phillips said Thursday's mountain top launch was the last key event in the fundraising and "time was running out".