Before the advent of the internal combustion engine and earth moving equipment, ore salt was exploited in underground galleries, instead of the modern open pit mines. That made the exploitation very expensive and risky, so that mostly slaves and prisoners were hired to dig in the tunnels. After Second World War most salt mines terminated their operations and they were transformed into heritage sites open to the public. Salt mines, unlike other mines, have large tunnels and halls, where rooms or places of worship were sculptured.
Wieliczka salt mine, Poland
A church inside Wieliczka salt mine, Poland (Credit: placesandpalaces.tumblr.com)
Salina Turda, Romania (Credits: www.visualnews.com)
Khewra Salt Mines, Pakistan (Credits: Wikipedia)
A mosque in Khewra Salt Mines, Pakistan (Credits: Wikipedia)