The most remarkable representative in the Middle Ages of the cave of Trophonios was that in Lough Derg in Ireland, the purgatory of S. Patrick as it was called. The origin is obscure, but it sprang into notoriety through the publication by a monk, Henry of Saltrey, of the descent of a knight Owain into it. Owain had been in the service of King Stephen, and he made his descent in the year 1153. Whether there ever were such a person as the knight Owain, or whether he was a mere invention of Henry of Saltrey is uncertain. Saltrey's account is precise as to the various stages through which Owain passed, and it is a vulgar rendering of the common stories of visits to purgatory, of which Dante's is the highest and most poetical version. Lough Derg is among the dreary and barren mountains and moorlands in the south of the County of Donegal; in it is an island, with ribbed and curiously shaped rocks, and among these was supposed to be the entrance to purgatory. Giraldus Cambrensis, who wrote his "Topography of Ireland" in 1187, mentions the island in Lough Derg as among the wonders of Ireland. [Footnote: But there is no mention of it among the wonders of Ireland in the Irish Nennius.] It was, he says, divided into two parts, of which one was fair and pleasant, while the other part was wild and rough, and believed to be inhabited only by demons. In this part of the island, he adds, there were nine pits, in any one of which, if a person was bold enough to pass the night, he would be so much tormented by the demons that it was a chance if he were found alive in the morning; and it was reported that he who escaped alive would, from the anguish he suffered there, be relieved from the torments of the other world. Giraldus continues by telling us that the natives called the place Patrick's purgatory, and that it was said that the saint had obtained from God this public manifestation of the punishments and rewards of the other world, in order to convince his incredulous hearers. Numerous visitors to Lough Derg in the Middle Ages published the narrative of what they had there seen and undergone, and rivalled each other in the extravagance of their accounts. There was a monastery on Lough Derg, and the monks had the key to the entrance to the cavern, but no visitor was suffered to pass within without the consent of the bishop of the diocese, and the payment of a heavy fee. Among all the extravagance that was written by visitors about the purgatory, some retained their common sense, and perceived that there was either fraud or hallucination in the visions there supposed to be seen.