Ok, so this will require a cursory examination of each stone, since the runes on them aren't all facing each other. I'll just call this a DC 0 Search check that can be done as a free action, but you still have to be on the correct side of the stone to see the rune. So you'll basically have to run around and look at each one till you find the right one. You can look at the map and work out the optimal path through them all or whatever if you want, but this will probably take a couple of rounds (unless you get lucky). We'll let the dice decide which stone is the correct one, since I didn't even pick it yet.
So you can roll 1d10, then 1d9, 1d8, etc, till you get a 1. Each die roll will represent checking one stone, and when/if you roll a 1 it will be the correct one. Odds are you'll roll a 1 before you get to the last one... If not, that will be it.
If we did this by the rules, it would probably require a search check (full round action for each stone) or spot checks (move action for each stone). So I think I'm being fair about it... The Unapproachable East book actually says these stones move around also, so I'm not just making this shit up.
If you guys are ready, I guess we're just waiting for HoV/Xuuvosic to teleport you.
Also, I don't think I mentioned this before, but I'm going to say this Enveloping Pit has had the functions of a Bottle of Air incorporated into it by the goblins, since they actually lived in the thing.