Entrambasaguas is a small municipality in the autonomous community of Cantabria, in northern Spain. It lies about 25 km south of the Bay of Santander and covers an area of 43.2 square km, made up of six towns. The population was around 5,000 as of 2015, having nearly doubled since 2005. The municipality is first mentioned in 1210 and forms part of the rural region often called Green Spain.
The terrain is moderately mountainous. Entrambasaguas is the origin of the Aguanaz River, which once drove 23 watermills and merges with the Miera River. Limestone caves in the area contain Paleolithic rock art, and there are burial sites from the Bronze Age.
Iron was mined here from prehistoric times. The ore was used in the Royal Artillery Factory of La Cavada, which supplied the Armada, and the industry eventually brought some wealth to the area during the Renaissance.