Kannonji, the 19th temple of the pilgrimage is just a single, small hall located right next to temple 18.
It is actually probably much older than Iwakuradera (temple 18) and was probably originally located higher up the mountainside.
According to the legend the temple was founded by Gyoki, which would make it early 8th Century. The honzon is also attributed to him.
It is now a Shingon temple.