Mirrors in Buddhism are a symbol of how we perceive life, death and the universe. Mirrors reflect, with no bias or influenced perception, everything that they see. Buddhism says that the individual and the universe are one, made of the same elements. A mirror reflects both the individual and the universe.
Such symbols have gained so much importance that they have been blessed and housed in specific buildings. At the Kyoto Imperial Palace the shunkoden 「Sacred Mirror Hall, 春興殿」 was built to house the sacred mirror 100 years ago.
From a sign outside the building:
The shunkoden was built to place the sacred mirror on the occasion of the enthronement ceremony of Emperor Taisho in 1915.
Instead of a traditional thatched or tiled roof, copper plates were used in the construction of this building, in a similar style to buildings at the Tokyo Imperial Palace.
For more information, and lots of photos, see the Kyoto Gosho 「Kyoto Imperial Palace, 京都御所」 travel guide.
View this location on Google Maps.