Stroove Beach on the Inishowen Peninsula offers a rocky headland near the lighthouse, providing an accessible environment for snorkelers. The site features a reef topography with depths ranging from 1 to 5 metres, averaging 3 metres. Snorkelers can explore the kelp forests found along the rocky features. Entry is from the shore, and conditions are generally mild, though the area is subject to surf. Water temperatures fluctuate between 9C and 15C, and the site requires significant thermal protection due to the cold water. Visibility typically ranges from 5 to 15 metres. Facilities at the site include parking, toilets, and showers.

Kinnagoe Bay on the Inishowen Peninsula is a shore-access site known for the wreck of the Spanish Armada ship La Trinidad Valencera located offshore. Snorkelers can explore the rocky headlands situated at either end of the beach. Conditions at this site are variable, with moderate currents, surf, and surge present. The water temperature ranges from 9C to 15C throughout the year, requiring appropriate thermal protection. Hazards include cold water, jellyfish, strong currents, surf, and surge. Facilities available at the site include parking, toilets, showers, and equipment rental. This location is suited for intermediate snorkelers.

Downhill Rocks at the eastern end of Downhill Strand offers an accessible shore entry point for snorkellers exploring the rocky fringes of the Mussenden headland. This site serves as a safer alternative to more challenging nearby locations for observing cliff-side marine life. Conditions are generally mild, though snorkellers should be aware of potential hazards including jellyfish, sea urchins, and surf. Water temperatures fluctuate between 9C and 15C throughout the year, necessitating appropriate thermal protection. Species recorded around this area include various crabs, lobsters, sea stars, and several types of jellyfish. Facilities at the site include parking, toilets, and showers.

Mussenden Temple Shoreline features a rocky reef environment situated directly beneath the cliff base. Snorkellers can explore small sea caves carved into the shoreline. Access is via the shore, and the site is suited for intermediate snorkellers due to variable conditions. Water temperatures range from 9C to 15C throughout the year. Divers and snorkellers should be aware of potential hazards including boat traffic, rip currents, strong currents, and surf. Low visibility can occur, and the water is cold. Facilities available at the site include parking, toilets, and a cafe.

Portvantage Cove is a rugged, rocky reef located in Strangford Lough between the Downhill and Castlerock railway tunnels. The site is defined by dramatic underwater topography featuring large submerged boulders and thick kelp forests. Divers should be prepared for moderate currents, potential surf, and surge, with entanglement hazards present. Due to these conditions, the site is suitable for advanced divers. Shore entry is required to access the reef. Species recorded around this area include harbour seals, grey seals, catsharks, skates, various crab species, and tube worms. Snorkellers may also enjoy the site, which holds a 4/5 rating.

Castlerock Basalt Cliffs (West End) features basaltic rock formations and deep rock pools where the sandy beach transitions into a rocky reef. This shore-entry site is suitable for beginners, with depths ranging from 1 to 5 metres and an average of 2 metres. Snorkellers should be aware of icy water temperatures between 9C and 15C, as well as potential hazards including surf and strong currents. Species recorded around this area include catsharks, skates, various crab species, and jellyfish such as the compass and giant jellyfish. Parking is available nearby for easy access to the water.

Castlerock Pier and Rocks is a shore-entry snorkelling site located near the mouth of the River Bann in Strangford Lough. The topography consists of rocky areas surrounding the pier structure. Conditions at this site are variable, as visibility can be influenced by discharge from the nearby river. Water temperatures range from 9C in the winter months to 15C during the peak of summer. This site is suitable for beginners, though it is rated 2/5 for snorkelling activity. Divers and snorkellers should be aware of the influence of the river environment on local water conditions.

The Bann Estuary, located at the eastern end of Castlerock Beach, offers a unique dive experience where the River Bann meets the Atlantic. The site features long stone training walls and an artificial reef constructed from pier boulders. Divers can expect depths ranging from 3 to 7 metres, with an average of 5 metres. Access is via the shore, though conditions include moderate currents and visibility between 1 and 5 metres. Due to the presence of boat traffic, cold water, and potential rip currents, this site is best suited for intermediate divers. Facilities available on-site include parking, toilets, showers, a rinse station, and a local dive shop offering guided tours.