It's a really, really odd text. Basically, it's the story of an Irish monk sailing around with a bunch of disciples. But it's also this wacky Christian allegory - all kinds of bizarre and fantastic things happen. Strangers appear out of nowhere on various deserted islands and provide the monks with food, or instructions. The monks are searching for the Happy Land, but that's doesn't actually seem all that central - they don't really come across as goal-driven seekers in the way one might expect. Their schedule is dictated largely by the Christian holidays - where they'll celebrate Easter, etc. Also, their course is determined entirely by God. God regularly makes them circle an island for days without food or water before providing them with a safe landing. Saint Brendan tells his followers not to exhaust themselves too much with rowing, because after all, if the Lord wants them to get somewhere, they will. Actually, they keep coming back to the same places - the Island of Sheep and the Island of Birds.
This might sound kind of boring, and it's definitely on the dry side, but there is something really remarkable in these sparse chapters and the wacky adventures they describe. Sea monsters, a crystal pillar, Judas perched on a rock. Most of these events are related with threadbare descriptions and not much in the way of reaction or commentary. When they see the pillar, for instance, they spend quite a few days trying to sail right up to it, and then they inspect it rather thoroughly, taking its measurements, etc. They express their appreciation, "perform the divine office", and sail away. There's something absolutely delightful about Saint Brendan's equanimity throughout. Although he occasionally experiences fear, for the most part he's wholly imperturbable, calmly accepting each new wonder with thanks to God.
Apparently historians are still at work trying to figure out exactly where the sainted man went. Some suggest that he may have even discovered America. Because he most certainly DID actually travel. This text was written much later - maybe as early as 800 AD, but probably not earlier (St Brendan died around 570). Popular versions of his story had already been circling for centuries, and O'Meara says they were undeniably influenced by other epic voyage texts such as the Odyssey or the Aeneid.
In some ways, the book is like a catalogue of wonders, a la Calvino's Invisible Cities or the like. But given how meager the description is, that doesn't really seem like the right characterization. The lack of psychological details makes it difficult to read as a quest narrative, or a document of the changes in the protagonist as he experiences new things. But there is something just, well, charming about the book.
** This is why one doesn't generally get much work done in a library - you're surrounded by distractions, calling out to you from the shelves.