Okay, so I've been working on lighting up the ravine under Bitterwell, so it's safer. If you're topside, there's the set of double-doors set into the hill under the wall in front of the fort. Go through them, and down the stairs until you get to the large room with the sandstone roof. There's a little 2-high passageway in front of you, and just inside of that starts a path that's all cobblestone with a torch on each block. That marks out a path that will take you all the way to the bottom if you follow it.
I've tried to light up the branching caves coming off the ravine, and blocked off a few larger unlit paths. (I think I've used at least six stacks of torches so far) Usually, I try to leave a one-block "window" so you can see there's more behind the wall, if you want to explore and light up those areas. Areas with drop-offs that end in lava have been "guard-railed" so that you can see what's there, but can't accidentally fall into it. Exercise caution anyway, because I may not have found them all.
Also, there is apparently another ravine that almost intersects this one. There are a few short passages that connect the two. Check near the end of the lit ravine (where it starts to go up, and I think there's a lot of dirt and gravel there) if you want to see for yourself.
I'm planning on making an "Under-Bitterwell" in the ravine face. So we can have dwarfy homes carved into the rock on both sides, with railed walkways on several tiers.
Oh, also. I've been trying to do "farm duty" in Bitterwell when I'm on. Feed the cows/chickens/sheep, harvest and replant the wheat, gather pumpkins/melons, cull extra animals from the herds, etc. I'm dumping most extra food/animal stuff in the chest next to the cows - feel free to help yourself. There was a good amount of uncooked beef/chicken and shit tons of seeds in there, plus a little wheat for emergency feedings. Oh, and I whipped up a bunch of cakes, so replacements for the cake table are in that chest too. Extra pumpkins and melon slices I drop in the chest next to the little square patch that they're in.