Hundreds of people took part in a protest at the Hellfire Club in the Dublin mountains over a €19m development plan for the area.
South Dublin County Council wants to build a visitor centre to more than triple current visitor numbers to 300,000 a year.
Protesters with the Save Hellfire campaign include local residents, landowners, hill-walkers and conservationists.
They believe that the plan which includes the visitor centre with an 80-seater restaurant, a tree-top walk and staircase to the top of Montpelier Hill would be over-development.
There would also be larger car parks, which would require trees to be felled, although South Dublin County Council plans to plant additional trees in other parts of the area.
Elizabeth Davidson of the Save Hellfire group said the scheme is aimed at tourism, particularly cruise ships rather than Dubliners.
Local farmer Frank Doyle said people come up to the Hellfire Club for peace and quiet and that the plan would spoil that.
However, most local councillors, with the exception of People Before Profit and the Greens, are supportive of the development which was drawn up by the Council and Coillte.
Mayor of South Dublin Gus O'Connell said current car parking facilities are inadequate for 80,000 visitors each year and that "something needs to be done".
An Bord Pleanála has ruled that a full Environmental Impact Statement is needed and the council said this will be ready by the end of July.
The council added that the design proposal is being finalised.