Arenig Fach is a mountain in southern Snowdonia, north Wales.

The summit itself is known as Carnedd Bachgen, named after the ancient cairn, Carnedd y Bachgen (which lies just north-east of the summit), and is the highest point at the north end of a wide plateau.

The mountain rises from the Migneint moorland and looks like a bulky heathery "lump" from most directions.

However, its north-eastern face has steep cliffs with a small corrie lake, Llyn Arenig Fach, at their bottom.

[1] The last glacier occupation of this corrie is thought to have happened during the Loch Lomond Stadial.