These weathered stone walls, with their curious brick archway, have puzzled historians and archaeologists for generations. The structure consists of two sections of rubble-built wall, roughly 2 metres long and rising to about 4 metres high, with the inner faces revealing what appears to be an ancient doorway. Whilst the brick arch itself likely dates from the 18th or 19th century, the lower stonework hints at something far older; possibly the entrance to a medieval bawn about 2 metres wide.

The mystery deepens when examining historical records. The 1657 Down Survey map of Lynn parish shows two castellated structures in this area, where Lynn church and its graveyard now stand just 250 metres to the southeast. One of these may have been the original Lynn Castle, whilst the other could have been the remains of the medieval church. When Ordnance Survey officials examined the site in the 1840s, they struggled to determine exactly where the castle stood, noting that the surviving walls were “partly old & partly new” with some sections barely 18 to 20 inches thick. They suspected the castle proper stood at a different point entirely, with the surviving arch perhaps marking its original entrance and the surrounding walls forming some sort of medieval enclosure.

By 1910, the Ordnance Survey had changed their annotation from “Castle” to “Monastery (in Ruins)”, adding another layer to the site’s complex identity. The 1840 map suggests a possible castle building in the western corner of a quadrangular enclosure, which may represent the original medieval bawn. It’s likely that the actual medieval castle stood at the centre of this bawn before being demolished, with the enclosure later repurposed as a courtyard when Lynn House was constructed in the 18th or 19th century, built directly onto the southeastern angle of the medieval walls. Today, these fragments serve as a tangible link to Lynn’s medieval past, even if their exact original purpose remains tantalisingly unclear.