THE 18TH-CENTURY RUINS OF THE Royal Artillery Factory of King Carlos III is a must-see for anyone wanting to explore the Los Alcornocales Natural Park. A short walking trail starting from the historic town of Jimena de la Frontera will lead you along the well-kept remains of the canal that carried the water to the blast furnaces in the factory. This 600-meter-long structure built for the siege of Gibraltar sits on the bank of the Hozgarganta River. The scale of the construction is astounding, with thick stone walls sometimes carved from the rock itself and a depth of up to five meters.

The landscape around the trail that lines the canal offers great historical and natural highlights. On top of the hill right next to it sits the Castillo de Jimena de la Frontera, a 15th-century Moorish castle. The trail leads along unique rock formations and natural pools in the river, not to mention an abundance of flora and fauna. Eurasian otters swim in the river and vultures circle over the nearby pastures.