Listoghil, the central monument and focal point of the Carrowmore passage tomb complex close to Sligo in north-west Ireland, has been ruined, excavated and eventually partially restored. However, the chamber is preserved in its original position. The author examines the hypothesis that Listoghil was deliberately aligned to mark seasonal transitions equivalent to astronomical cross-quarter days. The methods include a horizon survey, the isolation of directional features in the monument, and computer modelling of the monument and skyscape. Folklore and legends around seasonal transits, locally, in Ireland, and in many and varied (and independently arising) contexts at temperate latitudes of the world, are seen as information sources complementary to data gathering and observation.