A couple of months ago I wrote an essay for my Patreon about the things found in a jinja, in which I talked about the contents of the main sanctuary, which is normally closed to everyone, including the priests. That description was of the “standard”, and so, as Shinto is characterised by different practices at different jinja, not every jinja is like that.
In this week’s Jinja Shinpō, there was an article about “gyokuden”, which are found in the main sanctuaries of some jinja. A gyokuden (the characters used mean “jewel hall”, but this use of “jewel” is simply a way to express extreme respect; the Tennō’s body is traditionally referred to as “gyokutai”, where “tai” means “body”) is a second sanctuary within the main sanctuary. It is built in the same architectural style as a main sanctuary, although it is, obviously, a bit smaller than the main sanctuary it is inside. The seat of the kami is within the gyokuden.
Why would you have such a Russian-doll style situation? The main sanctuary is, in origin, a space for the exclusive use of the kami, where the kami can be permanently present. Thus, people are, in principle, not permitted to enter the main sanctuary. However, in the Heian period (about a thousand years ago) there was a move towards performing the most sacred ceremonies inside the main sanctuary, in an area called the “gaijin” (“outer chamber”, not “foreigner”) that was separated from the “naijin” (“inner chamber”), where the kami was enshrined. Izumo Ōyashiro has this design, but in this case it is believed to date back even further. Yasukuni Jinja is also designed this way, so that formal veneration there actually takes place in the outer chamber of the main sanctuary.
The gyokuden was a further development of that idea, in which only the gyokuden was for the exclusive use of the kami, and so ceremonies could be performed in the rest of the main sanctuary. The article discusses Itsukushima Jinja, a World Heritage Site on Miyajima in Hiroshima Prefecture, as a particularly striking example. This jinja is famous for its beautiful buildings, which are built on stilts over the beach so that they appear to be floating when the tide comes in. The main sanctuary is particularly large, because it contains six gyokuden, each of which is itself large enough to be the main sanctuary of a typical jinja. Because the kami are enshrined within the gyokuden, the doors to the main sanctuary are latticework, so that it is possible to see inside — this is very unusual.
Gyokuden are a regional phenomenon, found mostly in western Japan, and they are particularly common in Hiroshima Prefecture, the old Aki no Kuni. In Tokyo, however, they are rare.
Of course, this situation does raise a question of definition. If the space is not exclusively dedicated to the kami, is it really the main sanctuary? Or is the gyokuden the “real” main sanctuary, with another building, maybe an outer sanctuary, around it? The right answer is the one that is most helpful in understanding the real situation, but it is not entirely clear what that is.