The Koukamon Gate has a function as the border between Okunoin (Inner House) and other buildings. The Okunoin is not open to the public.

The name of the Koukamon was the same as one of the twelve gates, which existed in the palace at that time. The Koukamon Gate is 2.2m high, and 1.8m wide. It is relatively small in this area.

Construction of Koukamon Gate is Ming dynasty (Chinese) style. It also is called Ryuugu-zukuri (Palace of sea God.) Therefore, this gate is also called Ryuguumon Gate. You will have another kind of impression compare to other gates.

Outside is colored vividly, white wall, fundamental color of black and gold stand out. It is told that the inside is waxed.

Also, it is told that charming angels are painted on the ceiling. You can peep at the Okunoin (Inner House) through the low roof.