Nendrum Abbey is generally regarded as the best example of a pre-Norman monastic site in Northern Ireland that still has ruins from the original buildings.
Thought to have been set-up by St Machaoi in the 5th century, it has also been linked to St Patrick in later sources. (In fact Saint Patricks grave is not that far away)
The monastery consists of three round dry-stone walled enclosures, one within the other, with evidence of industrial work being carried on outside.The central enclosure has a church ruin with sundial, the remains of round tower and a graveyard. The middle enclosure contains remains of huts and workshops.
If you are on tours of Ireland it is well worth the journey. The views themselves are spectacular.
Ireland Luxury Tours frequently takes clients to this site and allows them to soak up the atmosphere from a genuine 5th Century site.