It was not always so hidden. In 1992, during construction work on the course, the ground gave way and revealed the chamber below, its roof lintels suddenly exposed to daylight for the first time in centuries.

What emerged briefly from that collapse was a souterrain, a type of dry-stone underground passage or chamber built during the early medieval period in Ireland, typically associated with nearby settlements and used for storage or refuge. The Mullaghroe example had its long axis running east to west and was roofed with flat stone lintels laid across the walls in the corbelled fashion common to such structures. Rather than excavate it fully, the decision was taken to backfill the opening and cover it over again, this time with soil shaped into a putting-green. The chamber is now listed as inaccessible, which is something of an understatement: it lies beneath an active golf hole, its precise contents and extent unrecorded beyond what that brief moment of collapse revealed.

There is something quietly odd about the situation. Souterrains are not uncommon in Cork, and many have been excavated and documented. This one was essentially reburied by accident of circumstance and convenience, preserved in a way, but also rendered permanently unreachable by the very landscape feature built to cover it. Whatever objects or evidence the chamber might contain remain where they were left, the lintel roof intact above them, the fairway above that.