Grianan of Aileach is an ancient stone fort located in County Donegal, Ireland. It sits on a hilltop, offering stunning views of the surrounding landscape. The fort is believed to date back to the early medieval period and is associated with the O'Neill dynasty, who were prominent rulers in the region. The structure is circular and features a thick stone wall, which is about 5 meters high in some places. Visitors can explore the site and learn about its historical significance, as it played a role in the power struggles of ancient Ireland. Today, it is a popular tourist attraction.