The cave in Ireland known as an entrance to the Otherworld, or the “Cave of the Cats,” is Oweynagat.
Oweynagat lies within the Rathcroghan complex in County Roscommon, the traditional royal centre of Connacht. Its Irish name, Uaimh na gCat, means “Cave of the Cats.” The site is a natural limestone cave reached through a constructed souterrain, with stonework and ogham inscriptions near the entrance.
Medieval Irish traditions connect the cave with the sídhe, or supernatural Otherworld, and with Samhain, the festival associated with the seasonal boundary between ordinary life and the spirit realm. Stories describe dangerous creatures emerging from the cave, including destructive birds, monstrous pigs, and the three-headed Ellen Trechen.
The Morrígan is especially associated with Oweynagat. In Táin Bó Regamna, she emerges from the cave while bringing a cow to breed with Donn Cúailnge, the Brown Bull of Cooley. Rathcroghan is sometimes broadly described as the portal, but Oweynagat is the specific cave meant by “Cave of the Cats.” Tara and Newgrange are important Irish sites, but neither is this legendary cave.