The Honister Slate Mine company has been fined £15,000 with over £13,000 in costs for the unauthorised extension of its Via Ferrata on Fleetwith Pike in the Lake District.
Workington Magistrates Court imposed the fine after Natural England took the company to court over the move, the latest in a series of controversial developments in an area where many love to go walking
The late owner of the firm Mark Weir had also planned to install a zip-wire on the mountainside, a scheme opposed by groups such as Friends of the Lake District on the grounds that it might affect a popular walking route.
His partner Jan Wilkinson said the fine was "on the high side", but accepted the ruling.
Walkers heading up mountains in the area may benefit from some facilities at the mine, however, such as its toilets and the electricity generator it shares with the Honister Youth Hostel.
In addition to Fleetwth Pike, peaks that can be climbed from the Honister Pass include Dale Head, Robinson, Great Gable and Haystacks.