Perthi-Duon Burial Chamber

Llanidan is a community in the south of Anglesey, Wales which includes the village of Brynsiencyn (Welsh pronunciation). The parish is along the Menai Strait, about 4 miles north-east of Caernarfon (across the strait). The parish church of St Nidan is near the A4080 highway, a little to the east of Brynsiencyn. The ruins of an earlier parish church survive.

Trefarthen is a village in the community of Llanidan, Ynys Môn, Wales, which is 125.6 miles (202.1 km) from Cardiff and 209.2 miles (336.7 km) from London.Of historical and archaeological interest are a Georgian mansion and the possible site of a 16th-century house.

Caer Lêb is a Roman and mediaeval site on the Welsh island of Anglesey, west of Brynsiencyn. Its name means "Leaven Castle". It is a low-lying site near the Afon Braint with a double row of pentangular banks (some parts now levelled) and marshy ditches. The original entrance was on the east, other gaps are modern and caused by animals. Based on the excavation of a similar site elsewhere on Anglesey, it may date from the 2nd century BCE.Excavations in 1865 found structures within the enclosure, rectangular buildings on the east and a circular one on the south. Nothing of these can now be seen on the ground. Pottery from the 2nd century to the 4th century was found, and on the north side a layer of periwinkle shells and a mediaeval coin, under a layer of peat.There is a parking area, sufficient for 4-5 cars, by the roadside. A footpath goes southwest on a low ridge, some 2 metres above the Afon Braint, from Caer Lêb over stiles, past the site of the former stone circle of Tre'r Dryw Bach, some 800 metres to Castell Bryn Gwyn and on to the Bryn Gwyn stones and the A4080. 500 metres north-west along the road, by Pont Sarn Las (Green Causeway Bridge), the foundations of three round houses may be visible after a dry summer. A large settlement was recorded in the 19th century, and destroyed in the 1870s by agricultural improvement.

The Anglesey Sea Zoo (Welsh: Sw Môr Môn) is an aquarium and independent research and marine education centre on the south coast of Anglesey island in North Wales. Located just outside the village of Brynsiencyn, Anglesey Sea Zoo claims to be the largest aquarium in Wales and displays over 150 native species.

St Nidan's Church, Llanidan is a 19th-century parish church near the village of Brynsiencyn, in Anglesey, north Wales. Built between 1839 and 1843, it replaced the Old Church of St Nidan, Llanidan, which needed significant repair, providing a place of Anglican worship nearer to the village than the old church. Some items were moved here from the old church, including the 13th-century font, two bells from the 14th and 15th century, and a reliquary thought to hold the remains of St Nidan. The tower at the west end has been described as "top heavy" and looking like "a water tower".The church is still used for worship by the Church in Wales, one of five in a group of parishes in the south of Anglesey. It is a Grade II listed building, a national designation given to "buildings of special interest, which warrant every effort being made to preserve them", in particular because it is regarded as "a distinctive example of pre-archaeological gothic revival work." The 19th-century clergyman and antiquarian Harry Longueville Jones said that it had been built in a "debased barbarous style, showing neither architectural science nor taste".

Castell Bryn Gwyn is a prehistoric site on the Isle of Anglesey, west of Brynsiencyn. It is a circular clay and gravel bank covered with grass, still some 1.5 metres (5') high and revetted externally by stone walls, which surround a level area some 54 metres (177') in diameter. Its name means "White Hill Castle".The original use of this site is uncertain although it may have been a religious sanctuary. Later Neolithic pottery indicates use in this period, and it may have been a henge monument at this time. The earliest bank and ditch belong to the end of the neolithic period (2500-2000 BC). During the Iron Age, the present wall was built, and it was refortified in Roman times and later.Parking is exiguous; the site is accessible from the A4080 by a footpath. Another path follows the low ridge, southwest over stiles to the Bryn Gwyn stones, or northeast, past the site of the former stone circle of Tre'r Dryw Bach, some ½ mile (800 metres) to Caer Lêb where it meets a minor road with limited parking space.

The Old Church of St Nidan, Llanidan is a medieval church in the community of Llanidan, in Anglesey, North Wales, close to the Menai Strait. The first church on the site was established in the 7th century by St Nidan, the confessor of the monastery at Penmon, Anglesey, but the oldest parts of the present structure, are now closed and partly ruined, date from the 14th century. In about 1500 the church was enlarged by the addition of a second nave on the north side, separated from the earlier nave by an arcade of six arches. During 1839 till 1843 a new church was built nearby to serve the local community, partly due to the cost of repairing the old church. Much of the building was subsequently demolished, leaving only part of the western end and the central arcade. The decision was condemned at the time by Harry Longueville Jones, a clergyman and antiquarian, who lamented the "melancholy fate" of what he called "one of the largest and most important [churches] in the island of Anglesey". Other appreciative comments have been made about the church both before and after its partial demolition. After that a new church was opened, the old church was used as a chapel for funerals for a period of time. It has been restored by the owners of the adjoining house, Plas Llanidan, and is occasionally open to the public. The remaining parts of the church are a Grade II* listed building, a national designation given to "particularly important buildings of more than special interest", in particular because St Nidan's is regarded as "a good example of a simple medieval rural church, enriched by 15th-century additions".In the 12th century, Gerald of Wales said that the church possessed a curious stone carving similar to a thigh that would always return by the next day no matter how far away it was taken. A Norman earl, he recounted, had chained it to a large rock and thrown it into the sea, only for the stone to return to the church by the following morning. A sandstone chest containing bone fragments, possibly are relics of a saint, were found buried beneath the altar. The chest and the church's 13th-century font were relocated to the new church.

Bodrida is an insular hamlet in the community of Rhosyr, Ynys Môn, Wales, which is 126 miles (203 km) from Cardiff and 210 miles (340 km) from London.

The Bryn Gwyn Stones (Welsh: Cerrig Bryn Gwyn) or Bryn Gwyn Standing Stones are neolithic stones in Brynsiencyn on Anglesey.

Afon Seiont (Welsh, meaning River Seiont in English) is a river in Gwynedd, Wales which runs into the Menai Strait. Its source is the outflow of Llyn Padarn near Llanberis, and it flows out in a generally northwest direction. Between the outflow and the village of Llanrug it is known as the Afon Rhythallt, changing its name just after the village. Its mouth is in the town of Caernarfon, forming a natural harbour as it flows out into the Menai Strait. The Afon Nant Peris provides the main inflow into Llyn Peris which then drains into Llyn Padarn with the addition of the waters of the Afon Arddu which drains the northern slopes of Snowdon. The name of the Roman fort of Segontium, near Caernarfon, is based on the Latinised form of the name 'Seiont'. In the Brythonic language *seg-ontio translates as "strong place".

Bodowyr Burial Chamber is a Neolithic burial chamber made of a few large stacked stones (also known as a dolmen or a passage grave) in a farmer's field on the north Wales island of Anglesey. It is located at Bodowyr Farm, 1.25 mi (2.0 km) east of Llangaffo, off the B4419 road.

Menai is the name of an electoral ward in the town of Caernarfon, Gwynedd, Wales. As the name suggests, it borders the Menai Strait. The ward elects councillors to the town council and Gwynedd Council.