The correct answer is the inner shrine.
Only the Imperial family and Shinto priests are allowed into the inner shrine. This is because Ise is seen as such a holy place and very sacred.
It is said that the Ise Shrine is the most sacred Shinto shrine in Japan which goes back to the 3rd Century. It is thought to be the spiritual home of the Japanese people and those who are Shinto.
The inner shrine is also believed to have the sun-goddess, Amaterasu.