Elidir Fawr

Marchlyn Mawr reservoir is a high level lake in Snowdonia behind Elidir Fawr mountain. It is used as the high level water source for Dinorwig power station, a closed-loop pumped storage hydroelectric generating facility. It is said that nearby lies the cave containing Arthur's treasure, a source of bedazzlement to the wanderer who sees it, and of disaster to the pilferer who touches it. The lake itself lies in between two mountains Carnedd y Fillast and Elidir Fawr and lies at a height of 636m above sea level and the reservoir took four years to build (from 1975 to 1979). The reservoir holds about 9.2 million cubic metres (320 million cubic feet) of water. From the reservoir, a 10.5-metre (34 ft) diameter tunnel runs for 1.7 km (1.1 miles) to a 10 m (33 ft) diameter vertical shaft. From the bottom of the shaft, a 9.45 m (31 ft) diameter tunnel leads to the power station, 670 metres (2,200 ft) away. It is possible to cycle up the road to the reservoir but a gate at the bottom prevents cars from driving on the road.

Mynydd Perfedd is a mountain in Snowdonia, Wales, forming part of the Glyderau. The summit has a shelter cairn, offering good views of Foel-goch's north-eastern face, and the Carneddau. Between it and Carnedd y Filiast, there are dramatic cliffs to the east, including the famous Llechen Cytrolar. To the south lies the parent peak Elidir Fawr, to the west Carnedd y Filiast and to the east Foel-goch and Y Garn. It is 812 metres (2,664 ft) high. The average annual temperature of the mountain is about 6 Celsius.

Carnedd y Filiast is a mountain in Snowdonia, Wales, forming part of the Glyderau. It, along with its top Y Fronllwyd (721 m), forms the most northerly summit in the Glyderau. The average annual temperature on Carnedd y Filiast is estimated to be around 4 Celsius.The summit is very rocky and has a number of cairns, as it has a vast expanse of layered slab of its crag features, giving rise to some exceptionally long, easy mountain routes, some giving over 1,000 feet of continuous climbing. Many routes are notable for their almost complete lack of protection and total isolation, and the summit affords good views of Anglesey, Snowdon, Carneddau, the Glyderau, Tryfan, Foel Goch, Y Garn and Elidir Fawr, along with Marchlyn Mawr reservoir. The Isle of Man and the Wicklow Mountains in Ireland can be seen on exceptionally clear days. It is about the 25th highest peak in Snowdonia.

Dinorwic quarry ( din-OR-wig; Welsh: [dɪˈnɔrwɪɡ]; also known as Dinorwig quarry) is a large former slate quarry, now home to the Welsh National Slate Museum, located between the villages of Llanberis and Dinorwig in Wales. At its height at the turn of the century, it was the second largest slate quarry in Wales (and thus, the world), after the neighbouring Penrhyn quarry near Bethesda. Dinorwic covered 700 acres (283 ha) consisting of two main quarry sections with 20 galleries in each. Extensive internal tramway systems connected the quarries using inclines to transport slate between galleries. Since its closure in 1969, the quarry has become the site of the National Slate Museum, a regular film location, and an extreme rock climbing destination.

Foel-goch is a mountain in Snowdonia, north-west Wales, and forms part of the Glyderau range, in Gwynedd. It lies in between Y Garn and Mynydd Perfedd.Good views of Dyffryn Ogwen are seen with Pen yr Ole Wen, Carnedd Dafydd, Tryfan, Glyder Fawr and Elidir Fawr close by. Its height is 831 metres (2,726 ft).

Y Garn is a mountain in Snowdonia, North Wales, part of the Glyderau. It is one of the Welsh 3000s — the 15 summits in Wales over 3,000 feet (914.4 metres) in height. It is the tenth-highest peak in Wales. Moderate snow accumulations can take place on the western-sloping side of the mountain from October to May. The south-westerly side of the mountain slopes gently down to the Nant Peris valley. The other, north-easterly side is of a different character, consisting of two steep-sided cwms, Cwm Clyd and Cwm Cywion, and finally Llyn Idwal and Ogwen Cottage. Along the ridge to the north lies Elidir Fawr, while to the south-east is the top of the Twll Du and Glyder Fawr.In 2011 three people were walking on Y Garn when they went over a cornice overhanging a ridge. About 50 metres of snow collapsed when the cornice gave way creating an avalanche and a person died when they fell 150 metres.

Llyn Peris is a lake in Snowdonia, Wales, approximately 1.8 km long and situated close to the villages of Llanberis and Nant Peris, and the smaller twin of Llyn Padarn. The lake was formed glacially and is an example of a moraine-dammed lake. Llyn Peris is named after Saint Peris, an early Christian saint of whom little is known. The lake is flanked on one side by the mountain Elidir Fawr and the former slate quarry of Dinorwig. Above the opposite bank are the hills of Derlwyn and Clogwyn Mawr and a rock formation known as the Lady of Snowdon, due to its resemblance to a human face. The ruins of Dolbadarn Castle are also located on a mound above the lake. The lake now forms the lower reservoir of Dinorwig power station, and the administrative buildings for the station are situated on the lake shore. Water is released into the lake from Marchlyn Mawr (the upper reservoir) to produce electricity during periods of peak demand. This water is, in turn, pumped back to the upper reservoir using electricity purchased at off-peak periods. The water level of the lake therefore varies considerably, depending on UK electricity demand. Excess water from the lake drains into Llyn Padarn. During construction of the power station, when the capacity of the lake was increased considerably at this time, with the removal of a large quantity of slate waste, rare Welsh Arctic char fish were removed to four other lakes in the neighbouring Carneddau mountains, namely Ffynnon Llugwy, Llyn Cowlyd, Llyn Melynllyn and Llyn Dulyn, where they are still to be found. Although Llyn Peris itself was not restocked, some char have found their way back to the lake. Parts of the lake shore are designated as a Site of Special Scientific Interest for Glacial Geology.

The Penrhyn quarry is a slate quarry located near Bethesda, North Wales. At the end of the nineteenth century it was the world's largest slate quarry; the main pit is nearly 1 mile (1.6 km) long and 1,200 feet (370 metres) deep, and it was worked by nearly 3,000 quarrymen. It has since been superseded in size by slate quarries in China, Spain and the USA. Penrhyn is still Britain's largest slate quarry but its workforce is now nearer 200.

Dinorwig, sometimes spelled Dinorwic ( din-OR-wig; ; Welsh: [dɪˈnɔrwɪɡ]), is a village located high above Llyn Padarn, near Llanberis, in Wales. The name is shared with the fort of Dinas Dinorwig, also within the community of Llanddeiniolen, on a foothill 6 kilometres (3.7 mi) from Dinorwig village and 3 kilometres (1.9 mi) from the Menai Strait and also with Port Dinorwic, the anglicised name of Y Felinheli.

The Paddy Buckley Round, also known as the Welsh Classical Round, is a long distance fell running challenge in Snowdonia, Wales. The route is a circuit of just over 100 km long taking in some 47 summits. The Round has the reputation of being somewhat tougher to complete than its English Lake District equivalent, the Bob Graham Round. Although no official time limit is set, an arbitrary 24 hours is applied, although the first completer exceeded the original aim of 24 hours. Runners may start at any point on the circular route (finishing at the same place) and may run the course in either a clockwise or anticlockwise direction. The route takes in the well-known high mountain ranges of Snowdon, the Glyderau and the Carneddau as well as the slightly less visited ranges of Moel Siabod, the Moelwynion, Moel Hebog and the Nantlle Ridge. The route was devised by the eponymous Paddy Buckley and first completed in 1982 by Wendy Dodds. The selection of summits that must be visited is somewhat arbitrary and no rules appear to have been applied in selecting them. Generally, it takes in the major peaks of the ranges that are being crossed, then any minor tops that are passed along the way are also included. Some of these tops really are just bumps on the ridge and not really summits in their own right at all. The fastest known completion of the round was, for many years, by Mark Hartell in 18 hours 10 minutes. On 4 May 2008, this time was matched by Chris Near of Eryri Harriers. This old record was broken in July 2009 by Tim Higginbottom who completed the Round in a time of 17 hours and 42 minutes. This was further reduced in 2019 by Damian Hall with 17 hours 31 minutes, and again on 30 August 2020 by Matthew Roberts with a time of 16 hours 38 minutes. Kim Collison set a new best time of 16 hours 20 minutes in April 2021. A year later, in April 2022, a new record was set by Finlay Wild who completed the round solo and unsupported in a time of 15 hours 14 minutes.The women's record is held by Jasmin Paris with a time of 18 hours and 33 minutes, set in 2016.The book "The Welsh Three Thousand Foot Challenges: A Guide for Walkers and Hill Runners" describes a version of the route which avoids the slate quarries, which the fastest line utilises, and also suggests attempting it as a four-day backpacking (lightweight camping) excursion rather than a one-day run.

Mynydd Llandygái (also spelt Mynydd Llandegai, [ˌmənɨðˌɬandəˈɡai] ; from Welsh mynydd "mountain", Llandygai "Church of St Tegai") is a small, partly forested hill in Gwynedd, North Wales. It forms the start of the Glyderau ridge. It is also the name of the quarry village at the base of the hill situated at the edge of Snowdonia National Park at grid reference SH600656. The village lies at about 1,000 feet (300 m) above sea level and gets strong winds and above average rainfall. Many of the houses are spread along long roads rather than clustered around a point, giving the village a somewhat decentralised feel. However the village is distinguished by two parallel rows of semi-detached quarrymen's cottages constructed during the 19th century for workers of Penrhyn Quarry, which mined slate. The first mention of housing on the site can be found in the census of 1841. Each of the houses was provided with an area of land (approximately 1 acre) sufficient to feed the family. This arrangement is clearly visible on the map of the area. This can be contrasted with the situation in the South Wales coalfields or in the industrial Midlands where no such provision was made for the workers. Originally named Douglas Hill, the name was changed in the 1930s after the inhabitants decided that they did not want to associate with the name Douglas, namely part of the Penrhyn family surname. (See Baron Penrhyn.) Physically the village has changed little since it was originally built. The area to the south is mountainous and there are a number of slate and stone quarries in the vicinity.

The Dinorwig Power Station (; Welsh: [dɪˈnɔrwɪɡ]), known locally as Electric Mountain, or Mynydd Gwefru, is a pumped-storage hydroelectric scheme, near Dinorwig, Llanberis in Snowdonia national park in Gwynedd, north Wales. The scheme can supply a maximum power of 1,728 MW (2,317,000 hp) and has a storage capacity of around 9.1 GWh (33 TJ).