This paper presents an open-access dataset from the Alento River Catchment (ARC) in southern Italy, a strategic Mediterranean Critical Zone observatory integrating long-term environmental monitoring with an open-air laboratory. Long-term observations of weather variables, streamflow, reservoir water level, groundwater depth, soil water content, and soil matric potential are complemented by targeted field campaigns involving hydrogeophysical surveys, stable water isotope analyses, soil physical and hydraulic measurements, spectral measurements, and high-resolution UAV-based mapping. The principal value of the ARC dataset lies in the coordinated integration of continuous and campaign-based observations across multiple spatial and temporal scales and Critical Zone compartments, providing a basis for linking localized soil and subsurface processes with field- and catchment-scale hydrological responses. Since 2016, the ARC has been a component of the European TERrestrial Environmental Observatories (TERENO) network. The dataset includes both directly measured and derived products, with documented processing procedures, quality-control information, calibration results, and missing-data records. The principal value of the ARC dataset lies in the coordinated integration of continuous and campaign-based observations across multiple spatial and temporal scales and Critical Zone compartments. The combined observations can support the development, calibration, evaluation, and intercomparison of process-based hydrological and Critical Zone models, the evaluation of Earth Observation products, and the investigation of scale-dependent relationships among point-, field-, hillslope-, and catchment-scale observations. The complete dataset is openly accessible through Figshare under a CC BY 4.0 license. (Romano et al., 2026; <a href="https://doi.org/10.6084/m9.figshare.31229608" target="_blank" rel="noopener">https://doi.org/10.6084/m9.figshare.31229608</a>).