A Japanese city has a graffiti problem. It is graffiti in sand. The city wants tourists to stop writing messages on the city's sand dunes. It damages the dunes and stops people enjoying them. There were more than 3,300 cases of 'sand graffiti' in the past ten years. In January, two tourists wrote a 25-metre-long birthday message.

The Tottori sand dunes are famous in Japan. They are Japan's largest and longest dunes. The biggest is 50 metres high. They are 16 kilometres long. They are on the Sea of Japan coast. There are now signs to ask people to follow the rules. The city said: "We want to continue to protect views of the beautiful sand dunes."