Just outside Dublin are the gorgeous Wicklow mountains. These mirror the wonderous green landscape that is so famous in Ireland. In these mountains is the medieval monastic settlement named Glendalough. Glendalough is Gaelic for "the glen of two lakes", named after its picturesque setting. This place was founded in the 6th century with many of its structures still remaining. These include a round tower, cathedral and priest's house along with many of the headstones of the settlement's inhabitants.
This is one of the most famous places in Ireland with good reason too. It is a serene place with beauty and history. Walk around the stone remains in the green valley and you will feel like you are walking in a secret garden kept hidden from the modern world. This is a place to go if you are interested in Celtic history. Many of the tombstones reflect the changing beliefs from paganism to Christianity with thier engravings.
Make sure you take a walk on the many paths around the lakes including the long distance Wicklow Way. These let you enjoy the mountain scenary around the old town. Wicklow is often described as the garden of Ireland and this place will show you why.