The thermal waters contain high concentrations of sulfate, calcium, and sodium, which are traditionally believed to help with respiratory and skin ailments.
The pools were historically used by Roman settlers who recognized the medicinal value of the springs.
The water temperature at the source is significantly higher than the ambient temperature, often exceeding 50°C, requiring the mixing with river water in the outer pools.
The Cidacos River acts as a natural cooling system; bathing comfort depends on the proximity to the river's inflow points within the stone basins.
Termas de Arnedillo are natural thermal springs located along the banks of the Cidacos River in La Rioja, Spain. The site is uniquely characterized by free-access, rock-lined pools fed by mineral-rich waters that emerge from the ground at temperatures between 35°C and 52°C. The water is classified as hyper-thermal, bromium, and radioactive-lithic, traditionally utilized for its therapeutic properties regarding rheumatic and dermatological conditions. Visitors typically use a series of stone basins where cold river water and hot thermal springs mix to achieve comfortable bathing temperatures. The area is part of a wider regional project that promotes spa tourism alongside the Vía Verde del Cidacos, a disused railway line converted into a path for hikers and cyclists. While public pools are free, the site is situated adjacent to a commercial thermal hotel that provides more formal spa treatments and amenities. The geology of the area involves deep-seated groundwater circulating through Triassic rock formations, which accounts for the high mineral content. The location remains one of the few places in Northern Spain where high-temperature medicinal waters can be accessed in a completely natural, outdoor setting.
From the pedestrian bridge spanning the river for an elevated view of the pools against the mountain backdrop.
Bring water shoes to navigate the slick, rocky surfaces of the riverbed and pools safely.
Visit during the early morning to secure a spot in the basins, as the limited space fills up quickly during peak season.
Pack a towel and a robe, as there are no changing facilities or changing rooms at the free public pools.
Do not attempt to enter the pools closest to the source without testing the water temperature first, as it can reach scalding levels.
Open year-round, though pool accessibility may be restricted by the Cidacos River water levels during heavy flooding or extreme rainfall.
Swimwear is required; maintain quiet volume out of respect for other bathers; carry out all trash to keep the natural area clean.
