Montanejos is a small inland spa village in Castellon, set where the Mijares River cuts through pale limestone hills. It is not a polished resort, and that is part of the point: the village is a base for warm river bathing, canyon walks, climbing, and a little Moorish and 19th-century heritage.
The reason to come is Fuente de los Baños, where clear thermal water rises into a natural swimming stretch of the river. Around it are the tighter walls of the gorge, the climbing routes of Barranco de la Maimona, and rougher paths that feel far from the Mediterranean coast.
Montanejos works best as a slow day in the mountains or as an overnight stop if you want to hike and swim without rushing. Bring shoes that can handle rock, check access rules for the springs in summer, and do not count on public transport for anything outside the village.