The Nightingale floors, or uguisubari, were designed to make a chirping sound when walked upon. These boards were used in the hallways of some temples and palaces, the most famous example being Nijo Castle in Kyoto. Dry boards naturally creak under pressure, but these floors were designed so that the flooring nails rubbed against a jacket or clamp, causing chirping noises. The squeaking floors were used as a security device, assuring that none could sneak through the corridors undetected.
Nijo-jo began as a mansion built by Nobunaga in 1569. The castle Nijo-jo was erected in 1603 to be Tokugawa Ieyasu's headquarters when he was in Kyoto. The donjon was struck by lightning and burned to the ground in 1750. It was never rebuilt. Ieyasu's palace is filled with beautiful works of art and is very well preserved. The Ninomaru Palace was mainly used for administrative affairs and reflects this in the many offices and meeting rooms it contains. It is designated a National Treasure.
