A proposed visitor centre development at the Hellfire Club is necessary to cater for population growth, according to South Dublin County Council.
The council is seeking permission for a visitor centre, improved walking trails and a 75-seat cafe around the site which it claims will be a "gateway to the Dublin Mountains".
The council outlined its application at the start of an An Bord Pleanála oral hearing.
Architect Paul Keogh said the site already attracts 100,000 visitors a year.
"The projected growth in the population of Dublin and visitors to the city will of itself result in an exponential increase in the number of visitors to the Dublin Mountains in the decades ahead," he said.
"A do-nothing scenario is therefore not sustainable."
The area of Montpelier Hill and Massy’s Wood would get a number of graded walking trails, as well as a tree canopy walkway and a zig-zag ramped walkway from the car park to the visitor centre.
Mr Keogh said improved access and car parking facilities as well as a shuttle bus from Tallaght would improve access and reduce congestion.
Preservation works would be carried out on a number of national monuments in the area including the Hellfire Club itself.
He said the policy in designing the plan has been to do "as much as necessary and as little as possible".
However, a group called Save the Hellfire involving local groups, conservationists and hillwalkers has opposed the plans, saying they are an over-development.
The group has expressed fears that hundreds of thousands of extra tourists will damage the integrity of the site and interfere with wildlife.
The hearing has attracted 84 submissions and is scheduled to last three days.
