Mynydd Llwyn-gwern

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

{{Infobox mountain

| name = Mynydd Llwyn-gwern

| photo = Mynydd Llwyn Gwern and Mynydd Moel - geograph.org.uk - 1234667.jpg

| photo_caption = The summit of Mynydd Llwyn-gwern with Mynydd Model beyond

| elevation_m = 269.2

| elevation_ref = {{cite web|url=https://getoutside.ordnancesurvey.co.uk/local/mynydd-llwyn-gwern-powys--powys |title=MYNYDD LLWYN-GWERN, POWYS - POWYS (SY20 9EX) |access-date=10 September 2019 |publisher=Ordnance Survey}}

| prominence_m =

| prominence_ref =

| parent_peak =

| listing =

| language = Welsh

| pronunciation =

| location = Gwynedd, UK

| range = Cadair Idris

| grid_ref_UK = SH 7650 0466

| topo =

}}

Mynydd Llwyn-gwern or Mynydd Llwyngwern is a mountain in southern Snowdonia, Wales. It lies above the Afon Dulas to the west and the Nant Ffrydlan to the east. The summit is noted for a series of low pillow mounds.{{Coflein|num=301254 |desc=Mynydd Llwyn-gwern |access-date=29 September 2021}}

The Llwyngwern slate quarry on the west flank of the mountain operated from the 1820s until about 1950.{{crs-return}} In 1972, the quarry became the site for an experiment in green living.{{cite book|title=Sugar News|url=https://books.google.com/books?id=wpUcAAAAIAAJ|year=1979|publisher=Sugar News Press}} This has now developed into the Centre for Alternative Technology which occupies much of the quarry site. The centre built a wind turbine on the summit of Mynydd Llwyn-gwern.

It is one of the Dyfi hills.