Can I go to Tianyu Beach at will?

What you are asking is can you go to the beach of Sanya Tianyu Hotel? Of course.

Because there are regulations in Sanya, although it is a private beach of the hotel, visitors can enter at any time. Fences are not allowed on the beach, and you can use the beach without staying in a hotel. But you can't enjoy some beach facilities provided by the hotel, such as beach chairs, so you can go anywhere.

A beach is land along the edge of water or flat land above the water surface formed by sand accumulation.