Mynachlog-ddu (SN143306) is a village, parish and community in the Preseli Hills, Pembrokeshire, Wales.

The Welsh placename means "black monastic grange":[3] before the Dissolution of the Monasteries, the parish belonged to St Dogmaels Abbey.

[4] Mynachlog-ddu and the surrounding Preselis are rich in prehistoric remains.

[6] Carn Menyn is presumed to be the source of the bluestones used in the inner circle of Stonehenge.

In 2000/2001 a project was established to try to transport a piece of bluestone from the village to Stonehenge.