Echtra

An Echtra or Echtrae (pl. Echtrai), is a type of pre-Christian Old Irish literature about a hero's adventures in the Otherworld or with otherworldly beings.
Definition and etymology.
In Irish literature "Echtrae" and "Immram" are tales of voyages to an Otherworld. In general the "Echtrae" are set in a pagan context. In contrast the "Immram", though containing mythological story elements, are set in post-pagan Ireland, and the main protagonist is Christian, and the journey is usually by sea.
A point of contention in absolute definition exists in the case of "Immram Brain maic Febail". Despite the naming this tale is considered to form part of the "Echtrae" milieu, and may have been named as an Immram due to a conflation of Bran (Brain) and St. Brendan.
Generally, "echtra" was the Old Irish word for "adventure" (literally meaning an "outing".), as well as a cognate for the Latin "extra", The modern and middle Irish language word is "eachtra".
The Dictionary of the Irish Language notes alternative usage meanings in addition to the primary "expedition, voyage, journey" - these include "a warlike expedition", and the more general "tale", or "history".
Description.
Though Echtrai often involve a journey to an otherworld, the exact destination or journey can vary - voyages take place by sea in "Echtrae Conli"; in a journey underneath a lake in "Echtrae Laegairi"; or into a fairy mound ("Sidhe") in "Echtrae Nerai"; alternatively the story may not included such a journey but instead involve an interaction with otherworldly beings : in "Echtrae Nerai", set on Samhain, the hero Nera sees prophetic visions whilst in the presence of a hanged man; whilst in "Echtra Mac nEchach Muid-medóin", the hero Níall gains the sovereignty of Ireland by kissing a hag guarding a well.
Works.
Lists compiled from , : 
There are also visits to the otherworld undertaken by the hero Cuchulainn, including : "Forfess Fer Fálgae", "Fled Bricrenn ocus Loinges mac nDuil Dermait", and "Compert Con Culainn"