This is a view of the back side of the Kirtland Temple.   The central panal of the lower windows (the arched window) is the window of the Holy of Holies of the temple.  It was inside this window the Jehovah, Moses, Elias, and Elijah appeared to Joseph Smith and Oliver Cowdery (D&C 110).

The most upper windows (third floor) open into the fifth room where the vision given to Joseph Smith regarding the Celestial Kingdom (D&C 137) was given.