The corridor running along the rooms in the Ninomaru Palace has a specially constructed floor that makes a sound like that of a nightingale when you walk on it. This corridor is known as the Uguisu-bari corridor. This construction is actually an alarm system because it generates sound whenever anyone walks on the floor of the corridor, warning of the presence of an intruder even at night. The floor contains special fittings and clamps, called mekasugai that generate the sound. There are a countless number of these clamps (about 12 cm long) located between the beams that support the floorboards of the corridor. There are two spike holes in each of the clamps and each hole has an iron spike in it. When someone walks on the corridor above a clamp, the clamp moves up and down causing the spike to rub against the clamp, producing a sound like the cry of a nightingale.
Incidentally, the Daihojo Hall at Chionin Temple, employed by the Tokugawa family for official affairs, has an Uguisu-bari corridor similar to that at the Ninomaru Palace.
Uguisu-bari Corridor  
Uguisu-bari Corridor  
* The veranda of the Ninomaru Palace is off-limits
for viewing.
The sound of the uguisu-bari corridor (MP3 file) The sound of the uguisu-bari corridor (MP3 file)
The structure of the uguisu-bari corridor Uguisu-bari Corridor  
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