Cape Maeda on Okinawa's west coast is the island's most popular diving and snorkelling site, centred on the Blue Cave — a sea cave at the base of a coral limestone cliff that floods with vivid blue light when the sun is at the right angle. It is busy by any measure, with multiple dive shops running boats and guided snorkel tours from the steps cut into the cliff. But the underwater scenery justifies the crowds: bright coral, abundant reef fish, and the cave itself are all within easy reach of swimmers of modest ability.
The cape itself is scenic — the coastline here is rough limestone falling steeply to clear water, with good views north and south along the Onna Village shoreline. For certified divers there are deeper sites offshore with larger fish and occasional sightings of reef sharks. If you want to avoid the busiest times, arrive early morning or on a weekday. The dive shops on the access road hire out full snorkel gear and are efficient; you don't need to book far in advance except in peak summer season.