Braich-y-Ddinas
Q634054, United Kingdom
Braich-y-Dinas was an extensive hillfort at the summit of Penmaenmawr, one of the northernmost peaks of the Carneddau mountain range on North coast of Wales. It was once considered the best preserved and most complete hillfort in North-West Wales, but completely disappeared in the first half of the 20th century due to a massive quarrying effort by the Darbishire family, which overwhelmed and eventually destroyed all traces of it, despite efforts by the Royal Commission to save the site.
Archaeological site data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).