Porthdinllaen is a sheltered bay in Pembrokeshire, United Kingdom, defined by its extensive seagrass meadows and reef topography. This site is suitable for beginners, offering shallow dives with an average depth of 3 metres and a maximum of 5 metres. Shore entry is standard, with mild currents and visibility ranging from 3 to 10 metres. The habitat supports a variety of temperate marine life, including various reef fish and invertebrates. Divers should be aware of potential hazards such as boat traffic, jellyfish, sea urchins, and surf. Facilities including toilets and a cafe are available nearby. The site is also suitable for snorkelling and night diving.

Dorothea Quarry is a flooded slate quarry in Mid Wales, recognised as one of the deepest accessible freshwater dive sites in the United Kingdom. The site features steep quarry walls, submerged machinery, and industrial debris, creating a complex overhead environment. Depths range from 3 to 104 metres, with an average of 40 metres. Visibility is typically between 10 and 30 metres. Due to the significant thermocline, water temperatures drop from 16°C in the shallows to 4°C at depth. This site is suitable only for advanced, deep, or technical divers. Shore entry is required, and a drysuit with an appropriate undersuit is strongly recommended due to the cold water conditions.

Segontuim is a wreck dive located in Pembrokeshire, United Kingdom, resting at depths between 20 and 31 metres with an average depth of 27 metres. This site is suited for intermediate divers due to the moderate currents and entanglement hazards present on the structure. Visibility is typically limited to 5 metres, requiring careful navigation and the use of torches. Water temperatures range from 9C to 16C, necessitating appropriate thermal protection. Access is by boat only, situated 14 kilometres from the shore. The wreck provides a habitat for various temperate marine life, including reef fish and invertebrates common to the region. Guided tours and air fills are available locally.

Llanddwyn Island is a tidal island featuring rocky inlets and secluded coves. This shore-entry site is suited for intermediate snorkellers who can navigate moderate currents and surf. Water temperatures range from 9C to 16C, reflecting the cold conditions typical of the region. Divers and snorkellers should be aware of potential hazards including rip currents, strong currents, and low visibility. The site provides access to parking, toilets, showers, and a cafe. A typical visit lasts approximately 60 minutes. As a tidal location, the topography is best explored during high tide when the rocky inlets are fully submerged.

Criccieth Castle is a shallow shore dive featuring reef structures that provide a navigation challenge for divers. The site typically ranges from 5 to 8 metres in depth, though it extends to 30 metres in some areas. Conditions are characterised by mild currents and variable visibility, which can occasionally be very low. Divers should be prepared for water temperatures between 8C and 18C. Due to the risk of boat traffic, the use of a surface marker buoy is essential throughout the dive. Parking is available at the site, facilitating a straightforward shore entry for those looking to build experience in temperate marine environments.

The Kimya is a wreck site located in Pembrokeshire, United Kingdom, resting at depths between 10 and 15 metres. This site is suitable for beginner divers looking for a manageable wreck experience. Divers can expect mild currents and visibility ranging from 5 to 10 metres. Access to the site is strictly by boat, as the water edge features surf and shore breaks. Water temperatures fluctuate between 9 and 16 degrees Celsius, necessitating the use of a drysuit or thick wetsuit. Boat traffic is a primary hazard, so divers should deploy an SMB upon ascent and remain close to their guide or charter crew.

Porth Ysgaden is a sheltered horseshoe-shaped bay on the Llŷn Peninsula, Pembrokeshire, featuring rocky walls and shallow gullies. This shore-entry site is suitable for beginners, with depths ranging from 5 to 9 metres and an average depth of 5 metres. Divers can expect mild currents and visibility between 3 and 10 metres. The site is accessible via a slipway and offers parking facilities. Night diving is possible, with typical dives lasting around 50 minutes. Water temperatures fluctuate between 9C and 16C throughout the year. Divers and snorkellers should remain aware of boat traffic and potential entanglement hazards in the area.

Vivian Quarry is a flooded slate quarry in North Wales offering a contained, current-free dive within an industrial setting. The site features submerged quarry walls and artificial reef structures, with depths ranging from 6 to 19 metres. Visibility typically varies between 5 and 10 metres. Due to the overhead environment created by the quarry walls and potential swim-throughs, buoyancy control is essential. The water remains cold throughout the year, making a dry suit, hood, and gloves recommended. The site is suitable for beginners and supports night diving. On-site facilities include changing rooms, air fills, equipment rental, parking, and toilets, providing a convenient location for training and gear checks.