The bay faces south-west and lies between the headlands of Mynydd Rhiw to the west and Mynydd Cilan to the east. These craggy headlands have cliffs descending to the sea, and Porth Neigwl is said to be like a broad open mouth in the relief of south Llŷn. The name “Hell’s mouth” was given for that reason and because of its danger to sailors in times of storm, with great waves and a lack of shelter.
The long, straight beach stretches for about 4 miles (7 km) between the two headlands. Behind the beach are grassy dunes which form a notable sea-marsh. The River Soch briefly runs parallel to the shore before turning inland near Llanengan (the only nearby village) towards Abersoch.
The area is a Site of Special Scientific Interest.
At the far end of Llanbedrog beach lies Carreg y Defaid and is best reached along the beach, having explored the excellent rock pools below Mynydd Tir Y Cwmwd and admired the beach huts tucked up to the undercliff. Carreg y Defaid is a small offshore island with an associated headland, both formed from hard volcanic rocks punctuating the softer sedimentary cliffs. A fragment of poor coastal heathland occurs on the headland visited by Linnet and Stonechat. Around the headland there are low rocky cliffs with sparse lichens including the bright orange Maritime Sunburst Lichen and the Black Tar Lichen. The boulders around the headland and further to the east have a relatively low covering of Bladder Wrack. Sea watching is perhaps best in winter for seabirds and roosting shorebirds. A flock of Golden Plover frequents adjacent flooded fields.