This panoramic old hillside Zapotec stronghold was where King Cosijoeza fought off the Aztecs in 1496. It's 7km north of Hwy 190, from a turnoff just past Puente Las Tejas bridge 11km west of Tehuantepec. The last 2km to the ruins are a sweaty uphill walk through tropical woodland from the end of the unpaved approach road.
There may or may not be any staff in attendance: ask at Tehuantepec's tourist office before going and to check opening times after the 2017 earthquake.
The unrestored site includes the remains of two pyramids, a ball court, a 64-room palace-type complex, several tombs, a thick defensive wall and several caves.