Berw Wion is a waterfall on the Nant Berw Wion stream in the Blaencwm area at the head of the Rhondda Fawr valley in South Wales.

The stream's name reflects the landscape's character — berw means "boiling" in Welsh, suggesting the turbulent nature of the water.

The fall is also known as Pen Pych Waterfall and forms the dramatic centrepiece of a popular waterfall walk from the Penpych Woodland car park.

A well-graded track leads through forest to a fenced balcony viewpoint, where a smaller cascade sits directly below and the tall main drop of Berw Wion rises ahead.

A stepped path continues beyond the viewpoint to the base of the waterfall, and a steeper route climbs to the top of the escarpment above.

The valley contains several waterfalls in close succession, making it a rewarding destination for walkers of varied ability.