Location: Mibaru Beach is about a 30-40 minute drive from Naha. I'm not sure about public transportation as I didn't use it, but if you have a car, it's a worthwhile trip. The water is incredibly clear, and there are unique rock formations, making the beach beautiful. Parking is paid (500 yen).
Experience: You take an approximately 12-seater boat with a transparent bottom out to sea to observe underwater fish. The experience is relatively short, about 20 minutes, but you can observe various fish closely and clearly at four different spots. It's a slightly different feeling than seeing them in an aquarium. I think it's a great alternative for those who can't dive. The fish you frequently encounter have their pictures and names posted on the boat. The captain kindly explains things at the observation points, but only in Japanese.
Safety: Personal safety equipment like life jackets are not provided separately, but the boat has a roof and you can only sit, so it's not particularly dangerous.