Understanding how gases move through the Earth’s crust is key to identifying active faults and assessing seismic or environmental risk. In this study, we measured radon isotopes (²²²Rn and ²²⁰Rn), carbon dioxide, and other gases in soil, along with groundwater chemistry, in the Bojano Basin—a tectonically active area in southern Italy. This region is part of a complex mountain chain that has experienced both compressional and extensional tectonics. By analyzing where radon and CO₂ concentrations peak, we identified hidden faults beneath the surface. These gas anomalies match well with independent geological and geophysical data, suggesting that gases are moving up along fractures and fault zones. Water samples from springs also show distinct signatures, indicating both shallow and deep circulation systems. Our results show that combining soil gas and groundwater analysis is a powerful, low-cost method for locating subsurface faults and understanding how fluids move through the crust. This approach could be used in other seismically active regions to support hazard assessment and monitoring.