Castlepook’s evidence presents Ireland as a shifting ecological frontier, rather than a uniformly frozen landscape. Reindeer, mammoth and lemmings suggest open, cold-country habitats, whereas Derryvree’s sedgy wetlands point to environmental variety. The possibly cut-marked reindeer bone is especially intriguing because it may indicate a brief human visit without establishing settlement or a secure route of arrival. Later ice expansion may have erased crucial evidence, complicating conclusions drawn from absence. How should archaeologists combine cave assemblages, wetland records, palaeogeographic reconstructions and Upper Palaeolithic evidence to assess the likelihood, nature and timing of human incursions into Ireland during Marine Isotope Stage 3?