The round tower at Glendalough stands about 30 metres tall and dates from the 10th or 11th century, a beautiful and functional landmark that has defined the valley's skyline for a thousand years. The conical cap is original, which is unusual — most Irish round towers have lost their caps over the centuries. It stands at the heart of the monastic enclosure and is visible from most points on the valley floor.
The tower is not open to climb, but you can walk right up to its base and examine the stonework. The quality of the masonry is remarkable given its age: tight-fitted stone with minimal mortar, built to last and evidently having done so.