Underneath Gaza is a complex network of tunnels built by Hamas over the course of several years.
Also known as the "Hamas metro," the network has been described by the IDF as an underground city, which also expands beneath the borders and into Israeli communities near the Gaza border.
These tunnels were used to transport rockets and other weapons, as well as bunkers and Hamas command centers.
Other tunnels also exist underneath Rafah, the city along the Egyptian border, which are used to smuggle goods.
The discovery was part of continued operations by the 7th Armored Brigade's combat who have been operating west of Khan Yunis in the Hamad area.
The tunnel extends about four kilometers long and ends near the Erez crossing but does not cross into Israeli territory.
He then noted the immense investment Hamas has made in constructing these tunnels, which he believes may have cost the organization up to a billion dollars over fifteen years.
Military sources said that Sinwar had planned to fight from an underground fortified base called "Room 6" - a place equipped for a long stay.
In recent weeks, some reports have alleged that Yahya Sinwar had fled to Rafah or even into Egypt.
The underground routes run for about 10 km and pass under a hospital and a university.
Top IDF officials have told The Jerusalem Post that it will take years to eliminate the Hamas tunnel threat.
The country in question said it had heard the report from senior Hamas officials.
This might be the worst-case scenario for Israel, but it would be very risky for Sinwar because of the high probability of being caught by the Egyptians.
The family was told that the video was found in a tunnel or in a hiding place.