The entrance of Center 20 is located on the right side of the pillbox in a trench which is partially filled by rocks which have fallen off the camouflage. The entrance door has been completely removed.
At the end of the first branch of the corridor, near the curve to the right, you find the opening, now lacking its cover, of the emergency exit shaft. In crossing over it be very careful because it occupies the entire walking surface of the corridor.