The highest point of the trail on the mountains, dubbed the Fairy Castle, has been heavily damaged by the fire that occurred on Thursday night (March 20).

The Dublin 18 Scenery Appreciation group condemned the fire on Facebook, saying that it’s now a "sea of burnt out heather."

"Walkers were horrified this morning at the charred out state of our famous 5,000 year old passage tomb known as the fairy castle and its surrounding land on Two Rock," the group wrote.

"The Ticknock to Fairy Castle looped walk is our area’s signature upland hike and the fire on Friday has damaged much of its scenery. Also this upland part of the mountain is important habitat for red grouse and last week on an early morning walk to the fairy castle we saw many red grouse in what’s now burned out heather.

"Does biodiversity matter here?"

Walkers on the trail were heartbroken at the fire, with one person commenting "this is dreadful news."

Local Councillor Lettie McCarthy was also saddened by the fires, commenting, "Beyond sad, at a time when birds are nesting. Biodiversity does matter and it’s heartbreaking to see this amount of destruction."

"Tragic, its such a magnificent area for birds and wildlife and walking, all destroyed," another added, while another commented, "Yes that is/was a good place to come across red grouse. I hope they can survive."

 Dublin Fire Brigade confirmed that they responded to the fire, the cause of which is not known at this time.

"Firefighters were called to a gorse wildfire on the Dublin mountains in Glencullen last night [Thursday]," a statement from Dublin Fire Brigade said.

"Two fire engines remained on scene overnight and the fire is causing a haze on nearby roads. Rain expected later will help extinguish the fire."

* This article was originally published on Extra.ie.