On the slopes of Mount Qasyun which overlooks Damascus, a network of tunnels links a military complex, tasked with defending the Syrian capital, to the presidential palace facing it.
The tunnels, seen by an AFP correspondent, are among secrets of president Bashar al-Assad's rule exposed since the opposition toppled him on December 8.
"We entered this enormous barracks of the Republican Guard after the liberation" of Damascus sent Assad fleeing to Moscow, said Mohammad Abu Salim, a military official from Hayat Tahrir al-Sham (HTS), the dominant group in the alliance that overthrew Assad.
"We found a vast network of tunnels which lead to the presidential palace" on a neighboring hill, Salim said.
During Assad's rule, Qasyun was off limits to the people of Damascus because it was an ideal location for snipers -- the great view includes the presidential palaces and other government buildings.
It was also from this mountain that artillery units for years pounded opposition-held areas at the gates of the capital.
An AFP correspondent entered the Guard complex of two bunkers containing vast rooms reserved for its soldiers. The bunkers were equipped with telecommunications gear, electricity, a ventilation system and weapons supplies.
Other simpler tunnels were dug out of the rock to hold ammunition.
Despite such elaborate facilities, Syria's army collapsed, with troops abandoning tanks and other gear as opposition fighters advanced from their northern stronghold to the capital in less than two weeks,.
On the grounds of the Guard complex a statue of the president's brother Bassel al-Assad, atop a horse, has been toppled and Bassel's head severed.
Bassel al-Assad died in a 1994 road accident. He had been the presumed successor to his father Hafez al-Assad who set up the paranoid, secretive, repressive system of government that Bashar inherited when his father died in 2000.
In the immense Guard camp now, former opposition fighters use pictures of Bashar al-Assad and his father for target practice.
Tanks and heavy weapons still sit under arched stone shelters.
Resembling a macabre outdoor art installation, large empty rusted barrels with attached fins pointing skyward are lined up on the ground, their explosives further away.
"The regime used these barrels to bomb civilians in the north of Syria," Abu Salim said.
The United Nations denounced Bashar's use of such weapons dropped from helicopters or airplanes against civilian areas held by Assad's opponents during Syria's years-long civil war that began in 2011.
