This inland promontory fort occupies a spit of high ground that locals have long referred to as a 'Doon', a term derived from the Irish word 'dún' meaning fort. The site's naturally defensive position is enhanced by human intervention; a low stone wall cuts across the narrow neck of land that provides the only easy access from the northeast, effectively isolating the promontory from the mainland.

The interior of the fort presents a flat expanse, though nature has thoroughly reclaimed much of the space over the centuries. Dense vegetation now obscures many of the site's features, making archaeological interpretation challenging. Exposed rock formations dot the overgrown interior, but distinguishing between natural bedrock outcroppings and the weathered remains of ancient structures requires careful examination. This ambiguity speaks to both the age of the site and the way time and Ireland's climate have worked to blur the lines between the natural landscape and human construction.

This description of the Tullynavinn promontory fort comes from the comprehensive Archaeological Survey of County Donegal, compiled in 1983 by Brian Lacey and his team of archaeologists. The survey documented field antiquities across the county, cataloguing sites from the Mesolithic period through to the 17th century, providing an invaluable record of Donegal's rich archaeological heritage. Such inland promontory forts are relatively uncommon compared to their coastal counterparts, making this overgrown Doon an intriguing example of how Iron Age communities adapted defensive strategies to inland topography.