Pego Do Inferno (waterfall/lagoon)

The word pego, in Portuguese, means a deep pool in a river, a place where the water is so still and dark that its bottom cannot be seen. That explains the name Pego do Inferno, Hell's Pool. Rural communities across Portugal have given the same kind of name to deep, frightening pools, and this one, in the hills behind Tavira, earned its title through a combination of depth, shade and a reputation for danger. Today, the picture is much friendlier, but the name is a good reminder to treat the water with respect.

The pool lies in a narrow wooded ravine cut by the Ribeira da Asseca, a stream that rises in the low hills of the Serra do Caldeirão and runs toward the coast. At the top of the ravine, the water drops over a rocky lip in a few small falls, fanning over moss and stone before collecting in a basin of deep green. The rock here is limestone, and the water, which is rich in dissolved calcium, has built up deposits of tufa, a pale, spongy stone that forms around plants and mosses. The result is a landscape of smoothed ledges and curtains of rock, with ferns and small trees clinging to the sides. Pine, carob and cork oak grow on the slopes above, and the shade is welcome in the heat.

Visiting is mostly a matter of timing and caution. The best months are late spring and early summer, when the flow is steady and the water is cool but not freezing. In late summer, after months without rain, the stream can dwindle, and the pool may be low and murky, while after heavy rain it can rise quickly and become muddy. Swimming is popular, but the depth varies, the rocks under the surface are slippery, and the water can be much colder than the air, so enter carefully, never dive and keep a close eye on children. Because the pool is small, avoid using soaps, creams or insect repellent in the water, take all rubbish away and keep to the existing paths, which protects the tufa from erosion. Dogs are allowed, but should be kept under control.

The walk from the car park takes about ten minutes through pine woods, and it is easy for most people, though the last stretch is uneven. There are no cafes or toilets, so bring water and food. The site is free and open all day. It is best to arrive early, as the pool can become crowded in July and August, and to leave before dusk.

The pool combines well with a visit to Tavira, the quiet old town of the eastern Algarve, with its Roman bridge, churches and the boat trips to the island beaches. It suits families who like short walks, swimmers and photographers, and it gives a cool, green contrast to the coast.