Video report by Kate Lewis
Plans to expand a car park and create new visitor facilities at the base of Pen y Fan have sparked a debate among locals and tourists.
National Trust Cymru started work on improving existing facilities at Pont ar Daf, along the A470, on Monday - with the addition of 200 parking spaces and new facilities including toilets and signage.
There are currently less than 60 parking spaces at the site, which is a popular starting point for the 350,000 people who walk up Pen y Fan each year.
Parking has previously been free, but visitors will now be charged a fee of £7.50 per car, unless they are a member of the National Trust.
The charity said this will help it to maintain facilities and carry out important conservation work in the Brecon Beacons.
The plans - which were approved in 2017 - have attracted praise and criticism, with social media users expressing their views on Facebook.
Craig Walsh described the move as "well overdue", adding that the "toilet situation there is embarrassing when we have people from all around the world visiting".
Llinos Steel agreed, commenting: "This should have been done 20 years+ ago."
Lynn Buckley said: "We visited twice just before Easter and were surprised at how scruffy it was. Polystyrene cups scattered around, and vile toilets. Glad to hear that something better is planned."
Anita Denny praised the move, commenting: "Good, some of us have to live here. Charge them to go up there, help pay for the repairs to the paths. It'll be safer all round when the masses are away from roadside."
But others have slammed the plans, with some saying they don't go far enough and others complaining about the apparent lack of parking spaces for motorhomes.
Jonathan Morris said: "I think you are still going to need a bigger car park."
Steve Haywood commented: "Disappointing to see not even one parking bay for the UK's 400,000 plus motorcaravans who since Brexit spend six months of the year touring the UK."
National Trust Cymru said limited parking around Pen y Fan is causing problems as the number of visitors grows each year.
Disabled parking spaces will be provided, as well as parking provision for minibuses, coaches and cyclists and an area for emergency services.
New visitor facilities will include toilets with disabled access, a changing places toilet, and baby changing facilities - some of which will be available 24 hours a day. Improvements to signage, footpaths and information will also aim to help visitors plan their day.
The charity said the redevelopment will be carried out sustainably, using local businesses and materials where possible and designed to be in keeping with the natural surroundings of the area.
It will also include electric vehicle charging points, the planting of trees, space for those choosing to travel by bus or bike, and areas to accommodate other sustainable transport.
Lhosa Daly, Interim Director, National Trust Cymru, said: "We want to ensure everyone who comes here has a welcome fitting of this special place by providing a great start to a day out enjoying the nature and beauty found outdoors."
The work is expected to be completed by this winter, and the charity said disruption to current parking and facilities will be minimal.