Rock salt was discovered under Loulé in the 1950s and in 1964 work began to sink two access shafts. A gallery was cut between the shafts at a depth of 230m (30m below sea-level) to allow ventilation. The Campina de Cima mine then began exploitation using the pillar and stall method to supply the chemical industries. The highest annual production was over 124,000 tonnes of rock salt in 1989. There are now 35km of tunnels. The mine still produces rock salt under the name TechSalt. The mine is in the town, at the eastern end of Rua Combatentes da Grande Guerra. Visitors take an industrial tour with a guide at the full depth of the workings, following roadways past conveyor belts, cutting machines, excavators, lorries and large caverns. They see geological formations 230 million years old and learn about the development of mining processes and the uses of rock salt.