Koteshwar Mahadev Temple is a Shiva shrine northeast of Ambaji, visited for its old temple setting and natural spring. Pilgrims come to bathe at the water tank and add the shrine to a wider Ambaji circuit, especially when travelling by private vehicle or hired auto-rickshaw.
It is a small, local-feeling stop, not a monument to cross Gujarat for. Paired with Kamakshi Temple or Kumbharia, though, it gives a better sense of the sacred geography around Ambaji than the town centre alone can offer.