What is First Jedi temple?

The first Jedi Temple[3] was an ancient building established and maintained by the Jedi Order on Ahch-To. It was the first of many temples built throughout the galaxy, and one of the few that were not demolished by the Galactic Empire. Luke Skywalker came to live near the temple as a hermit after his apprentice and nephew Ben Solo turned to the dark side of the Force and destroyed his new generation of Jedi.[2]