O'Donnell Castle, located in Donegal, Ireland, is a historic fortress that dates back to the 15th century. It was built by the O'Donnell clan, who were prominent leaders in the region. The castle served as a stronghold and residence for the clan, showcasing the architectural style of the time. Today, O'Donnell Castle is a popular tourist attraction, offering visitors a glimpse into Irish history. The site features restored rooms and exhibits that highlight the life and culture of the O'Donnell family, as well as the broader historical context of Donegal during the medieval period.