I had to look up Blaen y Glyn, it's close to an area we know but never heard of that walk, looks very good 
Yes as I guess you know, it is not far from Pen Y Fan and is a beaut to walk around and even take in after walking up Pen Y fan as did myself and family last year.
Or just to spend a few hours walking up one side & down the other of the Caerfanill river. There must be around 6/8 falls as you walk upstream. Needs to be light cloud or sunny to get some nice pics, if you are into that. The waterfalls are lovely.
At SO061200 way up above Blaen Y Glyn there is a plane wreckage ( I have yet to go up there myself) .
Quote
Here is the wreckage of a WWII Wellington Bomber which crashed here on 6th July, 1942. All five of the Canadian aircrew were killed in the crash, and there is a memorial to them on the site. One of the engines can be found lower down in a gully. There is no path to speak of from this point....
https://www.focusmagazinesltd.co.uk/2012/03/blaen-y-glyn-walk/
