Sealed Shrine
From ROdyssey Wiki

A mysterious quest to eradicate evil at the root and clean a maze of his population teeming with perverted monsters.
We share with you the only picture we could have from the inside from other adventurers who die before telling us all the story.

To go you need to start by Prontera, get out at the right, then up, right and right again (It’s on the map you do the monk quest)
/navi prt_monk 192/169
You enter the warp, go up and then right.
Here you can start your mysterious adventure by talking to Friar Patrick to tell him you want to enter. Then, it’s time to venture into the unknown by clicking on the grave next to him.
Good luck and may you be back in one piece.