On moorland next to a small country road deep in Bannau Brycheiniog (Brecon Beacons National Park) is a giant standing stone made from old red sandstone known as Maen Llia.

Erected sometime in the Bronze Age roughly 3300 BCE-1200 BCE, it is a listed scheduled ancient monument. Its original purpose is long forgotten, but theories include it possibly being a boundary marker or a pointer to a certain celestial constellation just to name a few. Standing at 12 feet tall and 9 feet wide, it is suggested there may be more of this stone buried underground.

Legend has it that the stone moves to the Avon Llia River to have a drink sometimes. This probably stems from the fact the shadow it casts across the moorland reaches the river when the sun is low in the evenings. In recent years, an information board with the same shape as Maen Llia was put near stone to give visitors more history on the site.

There is a small lay-by on the road near the standing stone.