An ocean monument and a survival island at spawn! The island is not the only one in the vicinity, as there are a few larger ones just east from the spawn point. But the monument is the only one here, so it needs to be thoroughly explored.
An entire room of wet sponge inside the construction can be located at coordinates 171 44 158. But the biggest treasure (in the form of gold) is hidden inside a massive block at coordinates 150 42 174.