At nearly 2.5km in length, the iron trains of Mauritania are among the longest in the world.
Their journey extends between Zouerat - the largest town in the country's north, known for its iron ore mining industry - and the port city of Nouadhibou in the west, for a total distance of 652km. The trip, which cuts through the heart of the Sahara desert, can last as little as 16 hours if the train is empty of ore, and up to 20 hours if the cars are full.
Impoverished locals often risk jumping on to the train's cars to travel between towns to visit relatives. Sometimes, the trains also transport goods such as live animals or fruit.
High daytime temperatures and very low night-time temperatures complicate the journey, as does the dust produced by the more than 200 train cars, each carrying 84 tonnes of iron ore.
Travellers willing to pay can buy tickets for about $3 to board the last car of the train, offering some comfort, although most of these passenger cars are a half a century old and not cleaned frequently.