Caer Sidi is the name of a legendary otherworldfortress mentioned in Middle Welshmythological poems in the Book of Taliesin. The following poem of Taliesincontains the fullest description of the Briton “other world” that mythological literature can provide. It has been collated by Charles Squire from four different translations of the text, those being of Mr. W. F. Skene, Mr. T. Stephens, Prof. John Rhys, and D. W. Nash. Mr. T. Stephens, in his "Literature of the Kymri", calls it "one of the least intelligible of the mythological poems". Squire also provides an interpretation of the poem: Another few lines penned by Taliesin are sometimes connected to Caer Sidi, although they add little knowledge to what has already been stated in the verses above. These lines are contained in a poem called "A Song Concerning the Sons of Llyr ab Brochwel Powys" : This confirms that the "heavy blue chain firmly held the youth" was the seasurroundingAnnwn, the Welsh Otherworld, and it makes the point that its inhabitants were freed from age and death. It reveals that the "drink of the host", the white wine, was kept in a well. Three singing organs are mentioned, an addition to the revelry of Caer Vedwyd . The first line is also thought to suggest that Taliesin himself was a privileged resident of this country. Some clues are given in the poems as to where the island may be situated. Lundy Island, off the coast of Devonshire, was anciently called Ynys Wair, the "Island of Gweir", or Gwydion. The Welsh translation of the "Seint Grael", an Anglo-Norman romance embodying much of the old British and Gaelic mythology, locates its "Turning Castle", in the district around and comprising Puffin Island, off the coast of Anglesey. Some attempts have been made to give the fortress a physical location, e.g. as the island of Grassholm off the coast of Pembrokeshire, but Caer Sidi is more likely to belong to the class of otherworldly forts and islands so prevalent in Celtic mythology.
