Here, an old loop of the river has long since silted up, though it remains wet enough to trace its original course; approximately 10 metres wide and a metre deep. This ancient waterway creates a natural boundary around an oval, grass-covered area measuring roughly 80 metres from northeast to southwest and 40 metres from northwest to southeast.

At the narrowest point of this river loop stand the ruins of Harrison’s castle, a strategic placement that took full advantage of the natural defences provided by the water. The enclosed grassy area within the loop likely served as a bawn, the fortified enclosure that typically accompanied Irish tower houses and castles. These bawns were essential features of medieval fortifications, providing protected space for livestock, storage, and additional defensive positions during times of conflict.

Today, visitors to Doonbran Island near Stonepark can still observe how medieval builders worked with the natural landscape to create their strongholds. The combination of the river’s protective loop and the castle’s positioning offers a glimpse into the defensive thinking of the period, when natural features were as valuable as stone walls in protecting settlements. Though time has altered the river’s flow, the site remains a testament to the practical engineering of Ireland’s castle builders.