As you might expect, this small cave on the Altus Plateau has lots of ingredients for poison craftables and perfumes. It also has what might be the easiest two-boss boss fight in the game, and a unique opportunity to see into one of the other dungeons on Altus Plateau.
From the site of grace, continue north deeper into the cave — you’ll follow the tunnel for quite awhile, and go down a few small drops. Eventually, you’ll drop down next to a summoning pool. Activate it if you like — this is a good place to co-op for Rune Arcs, since the boss is close to the pool and easy to kill. Then continue north on the path, and look to your left. You should see a perfumer standing near a lantern with its back turned to you. Sneak up and take them out, then look south and east to the low ground — there’s probably another perfumer staring up at you (and maybe preparing to fling some perfume your way).
Jump down and kill the second perfumer, then look around the corner to the northwest to find a third enemy to eliminate. Then backstab or otherwise make dead the perfumer that’s sitting in front of the big flower nearby, and run around the flower to grab x5 Living Jar Shard from the corpse there (you can also snag some Silver Fireflies from the ground to the flower’s right side).
From the big flower, head north and you’ll find another narrow tunnel. Continue through it, and you’ll enter another large chamber. Head to the right side of the high ground and look down, where you’ll see yet another perfumer. On the other (west) side of the room, there are two chests containing x10 Living Jar Shard and a Perfume Bottle, but be careful — if you didn’t kill the large flower here, it will sometimes use a ranged attack on you while you’re messing with the chests.
Continue north to leave the small cavern and enter a much larger one, where one of those weird magic-ant-thingies like the one in Ansiel River (South) is hanging out. Bait its rock attack, hide just around the corner, and then run across the tree trunk (also grabbing the x3 Arteria Leaf) once the attack ends. Ranged characters can also target the thing’s head and kill it — it doesn’t have too much HP, and you can just attack it every time it stops doing its rock-throwing attack. This is worth doing mainly because it will make grabbing some items in the Altus Tunnel much easier.
Across the tree trunk is another small cavern with a bunch of materials and minor items, plus the fog gate that leads to Omenkiller and Miranda.