Do I need a passport and visa to go to Sanya?

No need. You don’t need a passport or visa to go to Sanya. Sanya is located in Hainan Province, China, and is not a special administrative region, so inter-provincial travel does not require passports and visas. According to the "Exit and Entry Administration Law", Chinese citizens entering and exiting the country must apply for a passport or other travel documents in accordance with the law. However, if Chinese citizens travel to other countries or regions, they still need to obtain a visa or other entry permit from the country of destination, unless the Chinese government has signed a mutual visa exemption agreement with other governments or the Ministry of Public Security and the Ministry of Foreign Affairs have other relevant regulations. In addition, Chinese citizens who enter or exit the country as seafarers or work on foreign ships must apply for a seafarer's certificate in accordance with the law.