T. W. Rolleston in the context of Killiney

Táin Bó Cúailnge (Modern Irish pronunciation: [ˈt̪ˠaːnʲ bˠoː ˈkuəlʲɲə]; "the driving-off of the cows of Cooley"), commonly known as The Táin or less commonly as The Cattle Raid of Cooley, is an epic from Irish mythology. It is often called "the Irish Iliad", although like most other early Irish literature, the Táin is written in prosimetrum, i.e. prose with periodic additions of verse composed by the characters. The Táin tells of a war against Ulster by Queen Medb of Connacht and her husband King Ailill, who intend to steal the stud bull Donn Cuailnge. Due to a curse upon the king and warriors of Ulster, the invaders are opposed only by the young demigod, Cú Chulainn.

The Táin is traditionally set in the 1st century in a pagan heroic age, and is the central text of a group of tales known as the Ulster Cycle. It survives in three written versions or "recensions" in manuscripts of the 12th century and later, the first a compilation largely written in Old Irish, the second a more consistent work in Middle Irish, and the third an Early Modern Irish version.

In historical Indo-European religion, the concept of an otherworld, also known as an otherside, is reconstructed in comparative mythology. Its name is a calque of orbis alius (Latin for "other world/side"), a term used by Lucan in his description of the Celtic Otherworld.

Comparable religious, mythological or metaphysical concepts, such as a realm of supernatural beings and a realm of the dead, are found in cultures throughout the world. Spirits are thought to travel between worlds or layers of existence in such traditions, usually along an axis such as a giant tree, a tent pole, a river, a rope or mountains.