Beddmanarch–Cymyran

Cymyran Strait (Welsh: Culfor Cymyran) is a strait that runs from Beddmanarch Bay in the north to Cymyran Bay in the south between the islands of Anglesey (Ynys Môn) and Holy Island (Ynys Cybi). At either end it opens up into the Irish Sea. The strait was first crossed with a permanent land-link by the Four Mile Bridge by the latest date of 1530. It was later crossed by the A5 London to Holyhead Road at Stanley Embankment in 1823, the North Wales Coast Line using the same embankment in 1848, and finally the separate A55 expressway in 2001. The area specifically between the Stanley Embankment and the Four Mile Bridge is often referred to as the Inland Sea (Y Lasinwen) and is almost a lagoon. The only settlement on the shores of the strait is Four Mile Bridge itself, although the town of Holyhead and the villages of Valley and Trearddur are close by.

The Stanley Embankment (known locally as the Cob) is a railway, road and cycleway embankment that crosses the Cymyran Strait in Wales, connecting the Island of Anglesey and Holy Island. It carries both the North Wales Coast Line for trains, which runs from Crewe to Holyhead and the A5 road between London and Holyhead. The embankment was designed by, and its construction overseen by, Thomas Telford and was named after the Stanley family who were significant benefactors to the area.Prior to its construction the fastest route to Holyhead from the island's mainland was via the old stone bridge at Four Mile Bridge (Welsh: Pontrhydybont/Pont-rhydbont/Pontrhypont). When the A5 road was being constructed between London and the Port of Holyhead a more direct route was needed. Construction started in 1822 and completed a year later and is a total of 3⁄4 mile (1.2 km) long. It is significantly wider at the base (35 metres) than at the top (10 metres). The embankment to Holy Island was constructed using rock and materials excavated from a site on the Anglesey side. A workers’ hamlet grew up around the artificially-created depression, which was nicknamed “the valley”. After work ended, the settlement remained developing into a medium-sized village known as Valley. A year after opening, the embankment was partly damaged in a storm in 1824.In the 1840s, the embankment was chosen to carry the North Wales Coast Line to the Port of Holyhead (rather than build an entirely new crossing). Work to significantly widen the structure was completed in 1848. To allay concerns that passing trains might startle horse drawn traffic using the embankment, a tall stone dividing wall was built between the road and the railway.The embankment remained the only major crossing between Holy Island and Anglesey for more than 175 years. In 2001 it was superseded by a new wider embankment, which was built as part of the final section of the A55 North Wales Expressway. The section completely bypassed Valley and the old A5 at this point. The new crossing, which carries the modern A55 dual carriageway, was built parallel to the Stanley Embankment, following its north–south alignment.

Ynys Benlas is a small islet situated in the Inland Sea (Welsh: Y Lasinwen), part of the Cymyran Strait between Anglesey and Holy Island. It measures approximately 65 metres (east-west) by 35 metres (north-south) at low tide and covers about 0.2 hectares. Its name translates from the Welsh for "blue top island", which is thought to derive from the fact that bluebells apparently flourished on it. Late nineteenth century Ordnance survey maps refer to the islet as Ynys Henlas, which translates as "old blue island" According to the Archaeological Journal (1844), the islet (referred to as Ben Las in the Journal) may have been an ancient signal hill.

Four Mile Bridge (Welsh: Pontrhydybont / Pont-rhydbont / Pontrhypont) is a village spanning both sides of the Cymyran Strait in Wales, connecting Holy Island with Anglesey, and is approximately three miles (5 km) southeast of Holyhead. The village is quite small and is split between two communities on the two islands. The larger portion of the village is the principal settlement in the community of Rhoscolyn which recorded a population of 542 in the 2011 census. A small part of the village is in the community of Valley, Anglesey. The village is about one mile (1.5 km) from Valley railway station, and is on the Isle of Anglesey Coastal Path. The village has a hairdressers and a pub named "The Anchorage".

Anglesey Aluminium was a joint venture between Rio Tinto and Kaiser Aluminum. Its aluminium smelter, located on the outskirts of Holyhead, was one of the largest employers in North Wales, with 540 staff members, and began to produce aluminium in 1971. It was built on the Penrhos Estate, 500 acres of which were sold by the Stanley family for the project. Up until its closure it produced up to 142,000 tonnes of aluminium every year and was the biggest single user of electricity (255 MW) in the United Kingdom.Alumina and coke shipped from Jamaica and Australia would berth at the company's private jetty in Holyhead harbour. This jetty is linked by a series of conveyor belts passing through tunnels to the plant. A spur rail link from the main North Wales Coast Line runs into the plant and was used for both receipt of raw materials and despatch of aluminium. The plant was powered from the National Grid and received most of its electricity from Wylfa nuclear power station 15 miles away. AA was used as a base load for Wylfa and saved the grid the cost of keeping a power station on standby. The power contract terminated in 2009, and the aluminium smelting operation was shut down as no new contract was negotiated. The aluminium re-melt facility initially remained open after the shut down of the smelter, but its closure was announced in February 2013. The company has announced tentative plans for a biomass plant on the site, but smelting operations have been halted and the plant mothballed until 2016.It was announced in September 2022 that the former Anglesey Aluminium site had been purchased by Stena Line, with their intention to use the site to facilitate an extension of Stena's existing operations of the Port of Holyhead. The sale included the spur rail line, the jetty in Holyhead harbour and the former conveyor tunnel linking the jetty to the main site.Near the smelter the Aluminium Powder Company (ALPOCO) produces aluminium powder, which is used in pastes, pigments, chemicals, metallurgy, refractory, propulsion, pyrotechnics, spray deposition and powder metallurgy. Adjacent to the site is the public access Penrhos Country Park.

Penrhos Country Park (also known as Penrhos Coastal Park) (grid reference SH2781) is a country park near Holyhead, on the island of Anglesey in Wales, United Kingdom. The park attracts approximately 100,000 visitors each year. It was opened in 1971 on the former Penrhos estate which was formerly owned by the Stanley family and at the time of opening the Anglesey Aluminium company. It is adjacent to the A55, on the Anglesey Coastal Path and also adjoins Beddmanarch Bay. Parts of the park are a Site of Special Scientific Interest (SSSI) and Area of Outstanding Natural Beauty (AONB).In 2016, Isle of Anglesey County Council gave planning permission to Land and Lakes for a holiday village development in the park. As mitigation, Land and Lakes would develop a nature reserve at nearby Cae Glas. Part of the financial case for development is to provide accommodation for workers at any new nuclear development at Wylfa nuclear power station, and as of 2022 development had not started.The park was voted "UK's Favourite Park 2022" in a poll organised by the charity Fields in Trust.

Penrhos was a large estate on Holy Island, Anglesey, in north-west Wales.

Valley was a rural district part of the administrative county of Anglesey, Wales from 1894 to 1974. The district was formed by the Local Government Act of 1894 as the successor to Holyhead Rural Sanitary District. It took its name from the village of Valley which lay at the district centre. The rural district was abolished in 1974, when the Local Government Act 1972 amalgamated all local authorities on the island into the single district of Ynys Môn – Isle of Anglesey.

Valley Station signal box is a Grade II listed, 2-story, timber built signal box located near the railway station in Valley, Anglesey. Located directly north west of the level crossing on the B4545 road, the Signal Box is thought to have been built in the middle of the 19th century as one of 15 new huts built along the Chester and Holyhead Railway. Clad with horizontal tongue and groove panelling, with large sash windows and a slate roof. The interior of the signal box remain unchanged and still features the original lever frames.

Valley railway station (Welsh: Gorsaf reilffordd y Dyffryn) is a railway station that serves the village of Valley in Anglesey, Wales. It is the last station before the western terminus of the North Wales Coast Line at Holyhead. It also serves the nearby RAF base and Anglesey Airport.

Valley (Welsh: Y Fali) is a village, community, and former electoral ward near Holyhead on the west coast of Anglesey, North Wales. The population during the 2001 census was 2,413, decreasing to 2,361 at the 2011 census.

Trefignath is a Neolithic burial chamber near Trearddur, south of Holyhead on Holy Island, off Anglesey in Wales. In its most complete form it included a large cairn covering three stone tombs, set on a small knoll. It was excavated between 1977 and 1979, revealing several phases of occupation with three separate burial chambers built in succession. It is a scheduled ancient monument, maintained by Cadw. Trefignath is adjacent to an alignment of small standing stones which extends some 350 metres northwestwards. Beyond these, some 450 metres from Trefignath, is the larger Tŷ Mawr Standing Stone.