Thanks for bringing this up. It's good to have a plan, and in reading about others' I'm remembering the forts I've already done but nearly forgotten. Like:
The fort built above ground. All workshops were in buildings made of wood. Roads linked the town together. The meeting hall was made of stone, with a wooden peaked roof. The apartments were made of glass blocks, held 18 rooms per level, and each room had 2 or 3 clear glass windows. The fort held until the invaders mounted their flying monstrosities and had their way with the helpless townsfolk. I should have known not to forsake the earth.
The fort of the caverns. Once the caverns were breached, I tamed them. Every invading beast met my military until the edges were walled plum, save a kill trap. Homes were cut into the stalagmites, the cavern floor was my hallway.
The volcanic fort. The bare volcanic obsidian reached high out of the earth and I carved away what did not suit me. The fort consisted of the remains of the hill around the volcano, or structures I could build connected to its sides. I left the cap open to the sky and drained controlled pools into stone channels over which sat my forge and furnaces, high above the grassy plain with windowed walls. Until I made a mistake. Two miners dissolved, joining with the liquid stone like perverse terran revenge. The valley filled with lava over the next two years, until I realized the lifeblood of the fortress might drain faster than it could fill.
The frozen castle. The ocean, deep and solid as wet microcline, was hollowed and carved into rooms. The ice it yielded built a towering castle above the surface, it's walls holding traps that allowed us to harvest the wildlife. But with few places where trees would grow and the cruelty of learning that the caverns below lay barren of life, we could not make enough beds to keep people happy.
The mug of doom. The thick, rounded tower could only be entered from below. Once inside, the trained eagles harried invaders as they climbed the naked stairway 12 levels. If they made it this far they enjoyed the challenge of traversing the 6-layer spiral track and its carpet of traps to get to the path that lead to the entrance to the fort - a path that took them through the thick handle of this tall mug. Observant and unstoppable invaders would have noticed that the gore-covered weapons along the outer swing of the spiral were of goblin-make, and the glass disks and copper screws of the interior were relatively untouched. Most of this juggernaut's predecessors seemed to have been keen on dodging into the open space between the pathways... the fools. However, forgotten beasts do not enter the body by the mouth, and our bottom was bare and inviting.
The fort so safe dwarves actually grew old. On a level plain with a calm stream, the pink wall of fluff had 6 inviting entrances, and one broad, bloody and messy one. Those narrow entrances held cage traps and were guarded by boars and observant birds, and the broad entrance merely trapped with weapons. Not good weapons, just good enough to take out the unarmored foes and stun the skilled ones. Once the edge entrances were triggered their bridges raised, leaving only the broad entrance. Those who made it through found an interior filled with unspoiled wilderness and an imposing square tower of bone, with only one way in - a hatch leading down. It's tunnel held only a few cages, just enough to hold the beasts that broke in the door. Inside the invaders found a stair leading up to the next level, forcing them to run around the perimeter of the tower to get to the next stair up. 9 stories it went, covered in enough traps to force a few to fall onto spikes, and others to imbed themselves in the fort's lesser-qualitied weapons and giant axes. The caverns remained sealed off, where over a dozen forgotten beasts held council. The adamant roots of the mountain, harvested and refilled with stone. The king's chambers looked out of gemmed windows to the volcanic chamber below. Every surface smoothed and clean, every child safe and educated, every belly full to bursting on the finest roasts, every foot covered in opulent woolen socks and shoes of the finest leather. Every dwarf bored enough to just leave the gates open and doors unlocked, to see how well those steel-clad monsters of war might manage themselves if they ever had a chance to spill even a drop of blood.
Next? I don't know, I'll figure it out as I go.