Caernarfon, United Kingdom offers 6 beaches perfect for sunbathing, surfing, swimming, and more. Caernarfon is known for Caernarfon Castle, a UNESCO World Heritage Site. The best time to travel to Caernarfon, United Kingdom, is from June to August, with average air temperatures around 15-20°C (59-68°F) and water temperatures around 14-16°C (57-61°F). Sandee provides detailed maps, photos, and reviews from fellow beachgoers to help you Choose Your Beach™ and plan your perfect beach vacation!