Japan's manhole covers are a special treat. Instead of being strictly utilitarian, manhole covers in Japan celebrate local color. The Nago cover below has ocean waves to highlight their fishing port. And Uruma City is known for bullfighting (which sounds awful at first. But in Okinawa the bulls just push each other around like sumo wrestlers, no blood or death involved like cockfights or Spanish bullfighting).
UPDATE: I've now seen the top manhole cover in different areas around Okinawa, so it must be a generic one that's not specifically for Nago. But I did come across this one at a park in Okinawa City: