Before construction work could begin at Coolbeg, archaeologists moved in and uncovered the traces of an Iron Age settlement that had been quietly buried in the ground for over two thousand years.

Excavated in 2006 under licence, the site revealed the remains of at least one round house, the standard domestic structure of Iron Age Ireland, typically a circular timber-framed dwelling with a thatched roof, ranging here between five and seven metres in diameter. There were also possible traces of a second round house nearby, along with a central oval pit whose original purpose is not recorded. Crucially, the settlement was unenclosed, meaning it lacked the surrounding bank or ditch that often defined Iron Age farmsteads elsewhere. Radiocarbon dating placed activity at the site across two broad phases: one spanning roughly 760 to 400 BC, and a second running from approximately 380 to 160 BC, suggesting the location was returned to, or continuously used, across several generations. The findings were published by Frazer in 2009.