The engineers who laid out this route in the 1830s carved directly through the rock, leaving a pair of short tunnels at Releagh that are unusual survivors from an era of ambitious road building in the Irish southwest. Each tunnel measures roughly 5.8 metres wide and 3.7 metres high, cut by hand through solid stone at a time when improving road infrastructure in Kerry was both a practical necessity and, for some schemes, a form of famine relief work, though the precise circumstances of this particular project are not recorded.

The 1830s saw considerable investment in Kerry's road network, opening up remote mountain passes to wheeled traffic and connecting coastal and inland communities in ways that had previously been impractical. Rock-cut tunnels of this kind, where the hillside is bored through rather than blasted away on either side, were a relatively uncommon solution even then, requiring careful planning and sustained labour. At Releagh, this pair of short tunnels is part of a small cluster; a longer tunnel lies to the south-east and a further short one to the north, suggesting that the route through this particular stretch of ground presented repeated obstacles to the road builders rather than a single isolated difficulty.