You mean the area below the lava? Never actually got there. But I'm more interested in a more dangerous top world with strange creatures and what not. Not sure really what settings is needed to create a world like that.
Maybe you should try different playstyle or some mods ?
Instead of playing dwarf in ground play humans and try to build town on ground.
Then try to make town without broken AI defense like bridges or moats. Instead of gates relly on soldier patrols, traps and defensive buidlings which will stall enemy advancement.
I personally these days only play as humans and i usually build small village with some kind of lord mansion, barracks and fort that works as village last line of defense and where usually non combatants take refugee while in siege or some other things.
I try to build actually proper village instead of heap of garbage. If someone is getting married then i try to place them in one building in which both have close to their work. Instead of building 3x3 workshops on ground with nothing else i build whole building with complete design plan, cellars etc according to workshop use.
Let's say i want to build still. I build building where parter level something like 4x7, where 3x3 is still, 2x3 is small stockpile for empty barrels/jugs close to still, stairs up/down where cellar is for finished product which is about 4x6 while top level is for most of empty barrels stockpile which is connected to that previous one which is refilled from bigger one. Aside from that i add small room about 3x3 or 4x2 to it for food from which ale will be made. Aside from that depending on my playstyle i add living room for dude who will be working in it or i build separate house near it. Then i build a roof to finish it. Not just flat roof but multileveled one in cone shape which takes a lot of resources and it is harder to build.
It is a lot of work but once you finish it, it gives a lot of satisfaction. Then you also start to think about other type of buildings like farms etc. and you realize that for example farmer wife could be good carpenter but teaching her part of farming would be more efficient in long run. In any case you can also build her small carpentry workshop behind house for her exclusive use.
As i learned over the years villages build that way are really really really satisfying to play. Especially since you know most of your dwarves and what they do thus when someone dies it feels different than just another urist death. Case of ware creatures etc also are more impactful in such case as usually there are multiple victims and your start to think about isolations, chaining people etc trying to figure out who was biten and so on.
Defense is such scenario is also a way different. Creating patrols, defense lines, choke points. Properly managing your squads, building watchtowers outside of city to stall enemy, militia training aside from regular army, shelters in case of total mayhem.
Then there are mods. I think best one at least for me is Dark Age.
http://www.bay12forums.com/smf/index.php?topic=132486.0
There are added shitload of creatures and new factions that are not on map but they can attack you and much more diverse in what can attack you. Spectres, monster packs etc.