:Pen y Boncyn Trefeilw

{{Short description|Mountain (646m) in Gwynedd, Wales}}

{{Use dmy dates|date=April 2022}}

{{Infobox mountain

| name = Pen y Boncyn Trefeilw

| photo = Trefielwpen.JPG

| photo_caption = Pen y Boncyn Trefeilw from Foel y Geifr

| elevation_m = 646

| elevation_ref =

| prominence_m = 57

| listing = Hewitt, Nuttall

| language = Welsh

| location = Gwynedd, Wales

| range = Berwyn range

| grid_ref_UK = SH 96255 28339

| topo = OS Landranger 125

| easiest_route =

}}

{{GB summits start}}

{{GB summits entry|Name=Stac Rhos|Height={{convert|630|m|ft|0}}|Gridref=SJ085335|Status=sub Hewitt, Nuttall}}

{{end}}

Pen y Boncyn Trefeilw is a subsidiary summit of Cyrniau Nod in north east Wales. It forms a part of the Berwyn range called the Hirnantau. It has two tops: Stac Rhos and Pen y Cerrig Duon. Pen y Cerrig Duon is now listed as a deleted Nuttall due to re-surveying.

The views from the summit are extensive, if unremarkable due to the featureless, flat moorland surroundings. The summit is marked by a small cairn, is which located only a few metres from a track road that continues on to the pass between Cyrniau Nod and Y Groes Fagl.Nuttall, John & Anne (1999). The Mountains of England & Wales - Volume 1: Wales (2nd edition ed.). Milnthorpe, Cumbria: Cicerone. {{ISBN|1-85284-304-7}}.