Features:

Newgrange is a Neolithic structure in County Meath, Ireland. It is about 1 kilometer north of the River Boyne and about 10 kilometers west of Drogheda (in County Louth), and is part of the Megalithic Bru na Boinne complex.
Image Caption 2: Map of the River Boyne Valley showing its historical sights.
Newgrange was constructed in circa 32nd century BCE by Neolithic Irish (see Wikipedia: Newgrange: History). The Neolithic Irish were NOT the Irish Celts (see also Wikipedia: Celts, Wikipedia: Insular Celts) who arrived in Ireland probably before or circa the 6th century BCE (see Wikipedia: Prehistoric Ireland: Iron Age (500 BC -- AD 400)).
Newgrange is older than Stonehenge (earliest conjecture for earliest construction circa 3100 BCE: see Wikipedia: Stonehenge: Stonehenge 1 (c. 3100 BC)) and the Giza Pyramids (earliest construction early 26th century BCE: see Wikipedia: Great Pyramid of Giza).
The purpose of Newgrange is uncertain, but it may have been religious (see Wikipedia: Newgrange: Purpose).
The megalith lying in front of the entrance has triple spirals or spiral triskelions. The triskelion is a motif with three interlocked spirals, curved lines, or legs with rotational symmetry.
The triple spiral was used in Neolithic Ireland, Bronze-Age Ireland, and Iron-Age Ireland when the Celts arrived probably before or circa the 6th century BCE as aforesaid.
Newgrange embodies alignment astronomy, and so is a monument of archaeoastronomy.
At sunrise on the winter solstice, sunlight beams down the main passageway and illuminates a chamber floor (see Wikipedia: Newgrange: Purpose). This alignment was almost certainly planned.