Level requirement: 68
The last resting place
Once you clear the Cave of Chaos, the Prayer Shrine is literally less than a hop, skip, and a jump away. Just take about one step to the south, and you'll see it.
You can heal your party for free here. (Plus, you can always come back if you want.)
Activate the Porter and head out again.
From the Prayer Shrine, walk west and south till you reach a dark brown circle. Walk to the center to enter a hidden demon town.