The Visio Tnugdali ("The Vision of Tnugdalus") is a 12th-century religious text reporting the otherworldly vision of the Irish knight Tnugdalus (later also called "Tundalus", "Tondolus" or in English translations, "Tundale"). It was "the most popular and elaborate text in the medieval genre of visionary infernal literature" and had been translated from the original Latin forty-three times into fifteen languages by the 15th century, including Icelandic and Belarusian. The work remained most popular in Germany, with ten different translations into German, and four into Dutch. With a recent resurgence of scholarly interest in Purgatory following works by Jacques Le Goff, Stephen Greenblatt and others, the vision has attracted increased academic attention.
The Latin text was written down shortly after 1149 by Brother Marcus, an Irish itinerant monk, in the Scots Monastery, Regensburg. He reports having heard Tnugdalus' account from the knight himself and to have done a translation from the Irish language at the Regensburg abbess' request. The story is set in Cork, Ireland in 1148.
The visio tells of the proud and easygoing knight falling unconscious for three days, during which time an angel guides his soul through Heaven and Hell, experiencing some of the torments of the damned. The angel then charges Tnugdalus to well remember what he has seen and to report it to his fellow men. On recovering possession of his body, Tnugdalus converts to a pious life as a result of his experience.
The Visio Tnugdali with its interest in the topography of the afterlife is situated in a broad Irish tradition of fantastical tales about otherworldly voyages, called immram, as well as in a tradition of Christian afterlife visions, itself influenced by pre-Christian notions of the afterlife. Other important texts from this tradition include the Irish Fís Adamnáin ("The Vision of Adamnán") and Latin texts such as the Visio Pauli ("Vision of Paul"), Visio Thurkilli, Visio Godeschalci, and the Tractatus de Purgatorio Sancti Patricii (an account of a visit to Saint Patrick's Purgatory).