Inside the secret cave hideouts used by Syrian rebels and families

Syria's civil war has been raging for four years, and there are no concrete signs it will end anytime soon.

Over 200,000 people have been killed and more than 11 million more have been displaced. The conflict is forcing combatants and civilians underground: Syrians are using massive cave complexes in the countryside as strongholds, meeting places, and defensive positions for battles.

Some of the caves are natural while others are artificial and recently excavated. They're used by combatants but also by civilians desperate to shield themselves and their families from the violence.

Looking inside these caves and tunnels shows us how brutal Syria's civil war has become.

Captions by Reuters and Christian Storm.