The corridor is 9.1 m long x 1.9 m wide at its widest point .
The corridor is covered by a half - vault ( 2.8 m high at its lower and 3.5 m at its higher point ) .
The corridor is 9.1 m long x 1.9 m wide at its widest point , and is covered by a half - vault ( 2.8 m high at its lower and 3.5 m at its higher point ) .