Chuquicamata, 16 km north of Calama, is the largest open-pit copper mine in the world by excavated volume — a hole nearly 5 km long, 3 km wide, and over 1 km deep, with terraces spiralling down the sides like a giant inverted ziggurat. The state mining company Codelco runs free guided tours of the rim several times a week; tours are booked in advance through Codelco's visitor centre in Calama and require photo ID.
The tour also includes the abandoned company town of Chuquicamata, evacuated in 2007 because of toxic dust from the mine, and a viewpoint over the gigantic open-pit operation. The whole visit takes about three hours and is the single most distinctive thing you can do from Calama. Sturdy shoes and a hat are essential; bring water.