To start out I should point out that the term "Holy of Holies" comes from the Bible and referred to the most sacred part of the Tabernacle, Solomon's Temple, Zerrubbabel's Temple, and the Temple of Herod. The term "Most Holy Place" is usually another name for the Holy of Holies. The room contained the ark of the covenant and could only be entered by the High Priest once a year. It was separated from "the holy place" by the veil of the temple. In this way, our current temple celestial rooms are somewhat comparable to the Jewish Holy of Holies. Still, the rooms are quite a bit different. This should be expected as the Jewish temples were Aaronic Priesthood preparatory temples while ours are Melchizedek Priesthood higher law Christian temples.
The Holy of Holies in our temples have some similarities to their ancient counterparts. They have limited access - the prophet and occasionally others can enter the room. They are also used for heavenly visitations. Anciently, the Holy of Holies was where Gabriel appeared and announced to Zacharias that his wife would give birth to John the Baptist. In today's Holy of Holies, the prophet may receive similar heavenly visitations and directions on how to run Christ's church.
You might wonder what else "Holy of Holies" is used for. Apparently it is used for the higher ordinances of the priesthood. Apostle James E. Talmage said that it is "reserved for the higher ordinances in the priesthood relating to the exaltation of both living and dead". See his book The House of the Lord for this information. There are several temple ordinances mentioned in the scriptures which aren't performed often or even talked about regularly. I suspect that some of them might performed in the holy of holies. Here is one such verse:
Therefore, verily I say unto you, that your annointings, and your washings, and your baptisms for the dead, and your solemn assemblies, and your memorials for your sacrifices by the sons of Levi, and for your oracles in your most holy places wherein you receive conversations, and your statutes and judgments, for the beginning of the revelations and foundation of Zion, and for the glory, honor, and endowment of all her municipals, are ordained by the ordinance of my holy house, which my people are always commanded to build unto my holy name.
And he shall be received by the ordinance of the washing of feet, for unto this end was the ordinance of the washing of feet instituted.And again, the ordinance of washing feet is to be administered by the president, or presiding elder of the church.
Lets leave this chain of thought and instead get to the architecture of the Holy of Holies and when they have been used.
You can consider the Kirtland Temple to have included a Holy of Holies. The assembly halls could be divided using curtains (essentially veils) and on April 3, 1836 the Melchizedek Priesthood pulpits were curtained off with Joseph Smith and Oliver Cowdery inside when Jesus Christ, Moses, Elias, and Elijah appeared to them, accepted the temple, and conferred priesthood keys and the sealing power. For this reason, I think you could consider the pulpits in the Kirtland Temple as an early Holy of Holies.
The original Nauvoo Temple included a sealing room identified as the Holy of Holies. This was room 1 or the clerk's office. It was a sealing room, clerk's office, and Holy of Holies. Apparently it was used so much for the higher ordinances that other rooms had to be used for sealings so the room could be used for the higher ordinances. See this article for more details. Here is a drawing of a sealing room in the original Nauvoo Temple from lds.org. Details of how the room looked are probably guessed, but it gives you some idea of what the Holy of Holies may have looked like.
I don't know if the St. George Temple had a Holy of Holies, but I suspect it at least had a sealing room occasionally used for that purpose.
The Logan Temple used to contain a sealing room sometimes used as the Holy of Holies. This was the Gold Room. The room had gold directly applied to the plaster walls using a hot iron. As you can see, intricate patterns were made on the walls. The curtain is covering a doorway leading into the southeast tower spiral staircase. Also, notice the stained glass window. The windows were removed when the temple was gutted and remodeled in the 1980s. You can see the windows in the Church History museum (and I think the Manti Temple cafeteria has some of them as well - they looked familiar last time I ate there).
|Logan Temple Gold Room - Sometimes a Holy of Holies|
|Logan Temple Gold Room - Sometimes a Holy of Holies|
The Manti Temple also included a Holy of Holies. This one is directly off the celestial room and is still in the temple. It has its door left open so you can see the room and is now officially a sealing room, although one you can't use. Apparently President Hinckley wanted the room kept special because of its history (according to temple workers at the Manti Temple who said the room is rumored to have been a Holy of Holies. As you can see, the room is extremely ornate. I particularly like the arched area above the altar and the intricate detailing used there. Even small details such as the door handle and the hinges on the door are covered in symbolic details. This really is a fitting Holy of Holies.
|Manti Temple Sealing Room - Sometimes a Holy of Holies|
IF ANY OF YOU LACK WISDOM LET HIM ASK OF GOD
THAT GIVETH TO MEN LIBERALLY AND UPBRAIDETH NOT
AND IT SHALL BE GIVEN HIM
THIS IS MY BELOVED SON HEAR HIM
The room contains other nice architectural details. Carved faces are found on the arches. Vines are found on the columns. Sconces, a chandelier(s?), and art glass windows bring a lot of light into the room. You can also see that the room has intricate carvings. Despite all of this, the room is remarkably restrained for a room with so many intricate details. In Talmage's book The House of the Lord he states that the Holy of Holies is
reached by an additional flight of six steps inside the sliding doors. The short staircase is bordered by hand-carved balustrades, which terminate in a pair of newel-posts bearing bronze figures symbolizing innocent childhood; these support flower clusters, each jeweled blossom enclosing an electric bulb. On the landing at the head of the steps is another archway, beneath which are sliding doors; these doors mark the threshold of the inner room or Holy of Holies. . .Talmage then describes the Holy of Holies:
The floor is of native hard wood blocks, each an inch in cross section. The room is of circular outline, eighteen feet in diameter, with paneled walls, the panels separated by carved pillars supporting arches; it is decorated in blue and gold. The entrance doorway and the panels are framed in red velvet with an outer border finished in gold. Four wall niches, bordered in crimson and gold, have a deep blue background, and within these are tall vases holding flowers. The room is practically without natural light, but it is brilliantly illuminated by a large electrolier and eight side clusters of lamps. The ceiling is a dome in which are set circular and semicircular windows of jeweled glass, and on the outside of these, therefore above the ceiling, are electric globes whose light penetrates into the room in countless hues of subdued intensity. . .
|Salt Lake Temple Holy of Holies|
I hope you found this interesting. You may comment but remember that this is on the internet and these are sacred rooms, so let's be restrained in our comments on this one.
Here is a picture of the Dome Room, the room above the Holy of Holies in the Salt Lake Temple. It is just used to access the ceiling lights above the Holy of Holies and has been used as a dressing room.
|Dome Room Above Holy of Holies in the Salt Lake Temple|
. . . the large Dome Room, thirty nine by forty four feet. On the south side are three oval windows, and opposite these on the north are semi-discs of pebbled glass looking down into the Celestial Room and set in the arches thereof. In the center appears a large dome, fifty one feet in circumference at its base and seven feet high. This is set with seventeen jeweled windows and may be readily recognized as the ceiling of the Holy of Holies . . . In each of these windows electric bulbs are placed, and it is from these the room below derives its beauty of ceiling illumination and coloring. The walls are hung with portraits of Church authorities. No specific ordinance work belongs to this apartment. . .For more information, please read James E. Talmage's The House of the Lord first printed in 1912.