My first successful fort (fourth fort I'd ever made; first three were experiments.
had this above-ground area. Walls and rooms and the like.
There was a large outer wall, and then there was an inner wall that protected the entrance.
I expanded one part of the inner wall to reach over a brook to protect my fishermen. Not wanting to block the brook flow, I used vertical bars.
My outer walls all had doors next to the raised drawbridges on all four sides. Sort of a little fast escape hatch feature, just in case.
Everything I ever wanted at the time.
A few sieges later, trolls started showing up. By this point, I'm looking at about eight different units of goblins and trolls approaching.
"Oh, no problem I'm sure. Goblins are a cinch, and those trolls are probably just like goblins only tougher."
My trick was to use chained animals just outside the walls to bait in the enemy close enough to shoot them full of holes with about a dozen champion marksdwarves on the roof of the outer walls.
They begin firing at one troop on the east wall.
On the other end, I'm getting messages about trolls destroying my doors.
I look over and see that my outer wall has had a bunch of holes punched through it.
Those trolls hulk-smashed my doors!
The front of my inner walls had double doors. Knowing those were now useless, I simply constructed walls behind them.
"Hah! Nobody's getting in n--"
?!
They Hulk-smashed my vertical bars over the brook!
My champs moved in and saved the day, but man...
Learning experience, yes.
No doors.
No bars.
Drawbridges only.
Final Destination.