Churaumi Aquarium. One of the world's largest tanks, with whale sharks gliding past a wall of glass. Entry is around ¥2,200 ($14). It sits about 2 hours north of Naha, so pair it with the Kouri Island bridges on a full-day drive or bus tour.
Snorkel or dive the Blue Cave. Boat and shore tours at Cape Maeda run around ¥4,000-¥5,000 ($25-$31) with gear included. Book a morning slot — the sea is calmer and the cave less crowded.
Day-trip to the Kerama Islands. Ferries from Naha take 35-50 minutes and cost from around ¥2,000 ($12) each way. Expect white sand, turtles and snorkelling straight off the beach.
Walk Shurijo Castle park, the seat of the old Ryukyu kingdom. Be aware the main hall burned down in 2019; the rebuilt hall is due to open during 2026, and the gates, walls and views are open meanwhile.
Eat local. Try Okinawa soba (thick noodles in pork broth) and sata andagi, the local sweet fritters. The food here is its own cuisine, not mainland Japanese.