We're back! I summoned another stone giant to help me clear out the east side of the outer vault.
Now the west side. There's a door leading to the rune (right side of the screen shot), but there's a room full of enemies on both sides of the rune. And a lot of enemies blocking the path to the rune. If I could cast apportation I'd bust in through the front door and inch my way close enough to steal it. I don't have spells, so I took a different approach.
I opened a path on the left side of the rune vault and let my summons whittle the enemy forces down. My berserkers would probably die to quickly if I barged in through the front door.
That was easy. Trog gave me a gift, while my trolls were doing all the work. If I lose too much piety from using BiA, I'll just clear another dungeon level and return.
This is an uncomfortable situation, so I hesitantly teleported out of there. The rune is right within my grasp, so I don't need to rush.
I ended up outside of the vault, but I got swarmed by a bunch of black mambas. They managed to do quite a bit of damage before dying.
I finally decided to go through the front door, since there aren't many naga left. I summoned a berserk iron troll and let it finish off the remaining naga. Now, to grab the rune!
There it is.
Runes are magic symbols that act like keys to the Realm of Zot. Entrances to the Realm of Zot are at the bottom of the dungeon (D:27). You need at least 3 runes to enter Zot, though there are 15 unique runes.
Runes:* Dungeon - Snake (serpentine), Slime (slimy), Swamp (decaying), Shoals (barnacled), Vaults (silver), Tomb (golden).
* Abyss - abyssal.
* Hells - Gehenna (obsidian), Cocytus (icy), Dis (iron), Tartarus (bone).
* Pandemonium, by guardian - Cerebov (fiery), Mnoleg (glowing), Lom Lobon (magical), Gloorx Vloq (dark), or randomly (demonic).
We got the rune! A greater naga appeared, so I ran away. I still managed to grab an artifact ring while running.
A teleport landed me in this area. I burned a spell book to celebrate our achievement (and roast a guardian serpent)!
I put the rune away and identified the ring. It's not that good, but I'll keep it.