Glendalough Monastery
Nestled in the Wicklow Gap, the monastic settlement dates all the way back to the 6th century, although the present buildings date from the 10th-12th centuries.  It survived Viking raids and English oppression until the 17th century.  However, people still continue to be buried there, as gravestones of more recent times are mixed in with legible dates back to the 1500's, and weathered, illegible ones most likely go much further back.