It says "We're entering today through a Robber's Tunnel, a tunnel that some believe was created in 820 AD by Caliph al-Ma'mun, when he was trying to break into the pyramid."
It is not very clear from the picture outside. You can have a glance of the other side (as part of Descending Passage) as well in OP's tour, but again not clear, the view is blocked by something there.