Now the temple is just a myth, a story from the past that some people treated like a legend. However, for Apollo, this place is no myth or just a story. It is one of the places inside the tower' RED list, a catalog that contains names of places that are labeled dangerous due to the secrets they hold. The empire usually put strict supervision to them though Apollo can definitely bypass it.
"Well even if this place didn't turn into a dungeon the magical equipment there could still be powerful artifacts"
There are some instances when notable places turn into dungeons, sometimes even becoming natural labyrinths. Even with the corroded mana inside, it is still a type of energy that nature could change or just follow the flow.
[Creator, aren't you worried that the mana inside had corroded everything?]
