Lying 12 kilometres east of Cartagena, La Union (Pronounced Lan Yon) was once the centre of the largest ore-mining area in Europe. La Union is quite a modern town, having sprung up in the second half of the 19th Century as a result of the increasing intensive mining activity of the last 100 years. This period is reflected in the number of Art Nouveau buildings in La Union and the mines, now closed, have their own recognition. The Mining Museum can be located in the Old Worked Lyceum Building and the collection comprises of mining tools, scale models and a display of minerals.

The history of this mining area begins in Roman times, when they found rich minerals in the area and the first mines were opened. These minerals were transported all over the Mediterranean, via the port of Portman, known to the Romans as Portus Magnus, which lies 9 kilometres along the coast. The Romans knew La Union by the same name as Portman for a time, as it actually was two villages called Herrerias and El Garbunzal. As the population grew, it was easier to join the two villages and they eventually became La Union. By the turn of the 20th century, the industrial town had nearly 40,000 inhabitants, with most men employed in the mines.

Life in the mines was harsh and wages were low and at the end of the First World War, many people left their hometown to seek their fortune in the larger cities. The mines fell into a recession and it was a few decades before these would reopen. New technology meant it was feasible to work the mines again and once again, La Union became a busy town. The mines finally closed in 1991 and once again the population went down as work was sought elsewhere. At present the inhabitants of La Union average around 15,000.

The terrain around La Union is rugged and dry and the old chimneys from the mines are clearly visible. Near the top of the hills, there is a hermitage of the Virgin del Rosario (the Patron Saint of the Town) which is a mirador (looking platform) where everyone can enjoy the view. The Virgin del Rosario has a fiesta held in her honour every year in May and in October there is another fiesta to celebrate the mining. La Union is also famous for the Cante de las Minas (Mine Songs) held every August. This special form of Flamenco singing (a deep singing) can be heard in the Market Building and artists come from all over the region to perform.

Modern day apartment blocks have now strung up on the outskirts of La Union, aimed at drawing in tourists. A Tuesday market brings in more visitors and extends down most of the main street. A separate fruit and vegetable market is held in a different area not far from the main market and sometimes little break-away stalls are found near by. La Union may be finished with the mining, but this lovely town is still well worth a visit.