There is no surface trace of it. You would not know it was there at all.

A souterrain is an artificially constructed underground passage or chamber, typically built during the early medieval period in Ireland, and thought to have served as storage space, a place of refuge, or both. The one at Dunbulloge was investigated by R. Caulfield in 1863, and later described in detail by McCarthy in 1977. What he found, or rather what the earlier investigation revealed, was a pair of stone-built beehive cells, each roughly 1.82 metres in diameter and 1.52 metres high, with their long axes running north to south. A creepway, the narrow connecting passage that forces anyone moving between chambers to crouch or crawl, joins the two cells. A lintelled passage, meaning one roofed with flat stones laid horizontally across the top, extends some 4.57 metres from the second cell. McCarthy observed that this passage may run beneath the north-west corner of the adjoining church, which adds a particular strangeness to the arrangement: a pre-Norman underground structure potentially threading its way beneath a later ecclesiastical building, the two quite different in date and purpose, yet occupying the same ground.