Glendalough (Gleann Dá Loch - Valley of Two Lakes) is a glacial valley in County Wicklow, renowned for an early medieval monastic settlement founded in the 6th century by St Kevin.
The round tower, built of mica-slate interspersed with granite is about 30 m high, with an entrance 3.5 m from the base. The conical roof was rebuilt in 1876 using the original stones. The tower originally had six timber floors, connected by ladders. The four storeys above entrance level are each lit by a small window; while the top storey has four windows facing the cardinal compass points. Round towers, landmarks for approaching visitors, were built as bell towers, but also served on occasion as store-houses and as places of refuge in times of attack
Reference: Wikipedia