noun
inside a castle; within the castle
Refers to the interior of a castle building or the area inside the castle keep.
城内の見学はガイドツアーで行われます。
Tours of the castle interior are conducted with a guide.
noun
castle grounds; area within the castle walls
Refers to the entire enclosed area surrounded by castle walls, including courtyards and outbuildings.
城内にはいくつかの庭園と資料館があります。
Within the castle grounds there are several gardens and a museum.