Twyn Cil-rhew is a summit at the north end of the ridge that runs north from Pen y Fan - the ridge splits in to Y shape, with Twyn Cil-rhew being on the west side of the Y, and Allt Ddu being on the east side of the Y.
It provided a good view looking up to the northwest to see the sunset - this is the start of it -
The low sun to the northwest was lighting up the north side of Pen y Fan and Corn Du with a distinct warm glow.
I spent the next twenty minutes or so climbing southwards in the direction of Pen y Fan, and got to another sort of summit just as the sun was almost down to the horizon - I found a sheltered spot, and watched as the sun slowly disappeared.