Sweet, i found a secret passage in joppa.
On another note: It appears that the waterlogged tunnel (that is under red rock), always contains a small sphere of negative weight.
That is because there is always some "Ancient Bones". Did you notice the miner's helmet too? Or the pickaxe? Ect? I'm pretty sure the sphere is with that junk. You just auto pick it up and don't notice it.
I noticed, i just didn't bother mentioning it because those are kinda useless and pointless to point out.
There is a LOT of area down there. At least 4 screens deep, and something like 9-10 screens north/south. So your looking at a potential 40 screens to search.
Edit: A bug related to the underground river. I went up some stairs along the path, and the last level had no stairs up or down on it. Looks like the stairs should have dumped me on the screen north of Joppa, but since that is a blank area it can't have stairs up or down.
That sucks.
On another note: It appears that the waterlogged tunnel (that is under red rock), always contains a small sphere of negative weight.
Wait, what? Really? I've never found it before. How far in?
It is under ancient bones, so it looks kinda like garbage, but white, and eactly the same as normal bones, so you might easily miss it.
Last few games it was 3-4-6 (dunno how far really) areas south of the starting point.
In joppa, go to the north-west water pool, and go to the 2nd topmost right tile of water. Use the "go down stairs button", surprise, you just found your way to the waterlogged tunnel (and if you go far enough north, you can get to red rock that way).