Mynydd Rhiw

Mynydd Rhiw

Mynydd Rhiw is a 304.9 m Marilyn on the Llŷn Peninsula in Gwynedd, above Rhiw and Porth Neigwl. Its prominence is 239.5 m. The high point is the rocks 3 m south of the trig pillar at SH 22850 29392. DoBIH’s 5 cm comparison refers to the flush bracket on the pillar, not its top.

Landscape, geology and archaeology

The rocky ridge gives clear-weather views across Porth Neigwl and towards Eryri. Mynydd y Graig and Mynydd Penarfynydd are separate ridges farther south. Clip y Gylfinhir is the distinct southern prominence associated with radar/radio equipment.

Hard volcanic and igneous rocks are interspersed with sedimentary layers. BGS identifies the Mynydd Rhiw Rhyolitic Tuff Member and doleritic sills in the local Ordovician sequence.

Prehistoric extraction and tool-making left quarry pits, hollows and waste. RCAHMW reports visits around 3650–3050 BC and favours mainly local supply, rather than extensive long-distance trade. The evidence does not establish continuous production throughout that period. Bronze Age cairns and historic boundaries also survive. Do not move stones, build shelters in cairns or disturb archaeological features. Later manganese mining at Benallt and Nant left remains in the wider landscape; old workings are not places to enter.

Summit routes

Southern road-end out-and-back

Start and finish at the southern road end, 52.824863, -4.635782. Follow the northbound track uphill towards the summit mast, then leave the access line for the rocky trig-point area and the highest rocks 3 m south of the pillar. Return along the same approach to the road end. Richard M1HAX recorded 2.0 km and 80 m ascent on 19 September 2025. Roadside space is informal and very limited: obey signs and keep gates and the mast service road clear.

Llanfaelrhys coastal and summit circuit

Start and finish at the rough Llanfaelrhys lay-by, SH212269. Follow the Coast Path through Penarfynydd farm to the headland trig, then the ridge and coastal path below Mynydd y Graig. Climb into Rhiw, take the signed footpath and tracks north, cross the wall stile near SH230291 and reach Mynydd Rhiw’s trig pillar, the summit point visited by the published itinerary. Make a tiny extra visit to the highest rocks 3 m south of the pillar, then return to the trig area. Rejoin the mast access track towards Clip y Gylfinhir, fork at SH227288 and cross the stone stile at SH223286. Descend the rough western pasture to the waymarked gate and walled lane. Turn left on the road, immediately right, then straight over the crossroads towards Porth Ysgo to regain the lay-by. Happy Hiker’s whole coastal circuit including the trig pillar was walked on 12 May 2015 and is listed as 7.3 miles, approximately 11.7 km. The western descent was vague and gorse-obstructed; use the full guide, current map and signs, and check parking and access.

Separate lower-level walks

The National Trust’s Plas yn Rhiw and Rhiw village walk is a 3.68 km base circuit taking about an hour. It goes through woodland and Rhiw village and returns by lanes. Gwynedd’s different Rhiw Circular Walk is 4.3 km and about two hours, following the south-eastern hillside through fields, lanes and woodland. Neither reaches the summit, and their metrics must not be applied to a summit ascent.

Access, facilities and safety

The short southern summit walk was recorded from the road end at 52.824863, -4.635782 in September 2025. Its author described very limited verge space; this is not a verified formal car park. Keep gates and the mast service road clear and obey current signs. Happy Hiker’s longer circuit started at a rough Llanfaelrhys lay-by, SH212269, in 2015; availability and permission need checking. Plas yn Rhiw visitor parking, SH237282 in the National Trust guide, serves the separate lower village walk.

Gwynedd’s current bus index links Berwyn routes 17/17B between Pwllheli and Aberdaron; the 17B variation serves Rhiw. The linked timetable is effective from 12 April 2021, so check the operator or Traveline for your travel date, stop and return journey. Do not assume Sunday service or a bus to the summit trailhead.

Plas yn Rhiw below the hill has toilets and a tea-room; check opening times before relying on them. The house remains closed throughout the 2026 season for essential restoration, which does not establish a closure of the hill. Carry water and food for the summit routes; the longer Llanfaelrhys circuit has no facilities identified by its route author.

Expect uneven paths, gates and stiles, slippery rock and grass after rain, and exposed wind or poor visibility. The longer circuit adds coastal slopes, several track junctions and a rough descent through gorse. Take care on road sections, give livestock space and follow local dog-lead requirements. Check current signs and access notices before setting out.

Sources and dates

Research checked 17 October 2026. DoBIH row revision, source publication dates and actual walk dates are distinct. The catalogue’s imported revision is retained; the source row used for factual corrections is DoBIH v18.6, record 1955, revision 23 February 2025, with no physical survey date inferred.

• DoBIH / Hill-bagging record 1955
• National Trust village walk
• Gwynedd Rhiw Circular Walk
• Happy Hiker summit/coastal circuit, walked 12 May 2015
• Recorded southern walk, 19 September 2025
• RCAHMW Neolithic axe-factory record
• BGS Rhiw geological study
• National Trust visitor information