Termas de Río Hondo is a spa city in Santiago del Estero Province, Argentina. It has 27,838 inhabitants as per the 2001 census. It is loca…Termas de Río Hondo is a spa city in Santiago del Estero Province, Argentina. It has 27,838 inhabitants as per the 2001 census. It is located on the banks of the Dulce River, 65 km north of the provincial capital Santiago del Estero, near the artificial Río Hondo Lake.