The ancient monument in England aligned with the winter solstice sunset is Stonehenge.
Stonehenge stands on Salisbury Plain in Wiltshire, England, and its principal axis follows the Sun’s seasonal extremes. The monument’s great trilithon horseshoe, Heel Stone, and avenue are aligned broadly toward the point where the Sun sets at midwinter. The opposing direction corresponds to sunrise at the summer solstice.
The alignment reflects the changing position of the Sun along the horizon during the year. Around the winter solstice, the Sun sets at its most southerly point and daylight is shortest in the Northern Hemisphere. Stonehenge’s builders could have used the axis to mark this turning point, although the monument’s exact religious and practical purposes remain uncertain because its builders left no written records.
Newgrange and Maeshowe are frequent mix-ups. Both are important prehistoric monuments with strong solstitial associations, but they are not in England: Newgrange is in Ireland and Maeshowe is in Orkney, Scotland. Avebury is also in Wiltshire, yet Stonehenge is the standard answer to this question.