Gargantua, the giant, is said to have used this chamber as a bed. Maybe he liked sharing his bed with a few fairies!
See - The Life of Gargantua and of Pantagruel (in French, La vie de Gargantua et de Pantagruel) a connected series of five novels written in the 16th century.
The chamber would originally have been between sixteen to eighteen meters in length, but is now reduced to only five and a half meters. There are currently half a dozen covering titles.