My best fort was a green glass castle, in a scorching hot desert, with a cavern and a magma pipe. Captured and tamed giant bats, and a pair of giant spiders (was sad that they couldn't breed, but it was awesome to watch them slaughtering Gobos). Also captured a pair of fire imps, but they were never more than a curiosity- caged and put on display. The whole fortress was made of glass, and the temperatures of the desert were so extreme that all the walls were "warm green glass walls." Booze would evaporate as soon as the traders arrived, and even leather would melt if it was left outside when summer came.
The fortress was attacked by a dragon, after a while, whose flaming breath melted green class roads, and set a fire burning in the Trade Depot which kept burning for months and months, completely destroying the Depot and its contents, leaving nothing but puddles of various materials. On the upside, it got rid of all the sticky molten leather: on the downside, it melted the bars of gold and silver, and precious metal goods that I had been trading for, due to a general lack of valuable metals in that fortress.
Also built my favorite traps there: a deadly glass forest. A support, which propped up a pile of green glass blocks and ramps arranged to look like a tree, or giant mushroom, was surrounded by pressure plates linked to the support. This was repeated to make a forest outside of my outer wall. When goblins set foot in the forest, it came crashing down on top of them. Those who escaped the carnage of the glass forest, had to face a hail of bolts (usually goblin bone bolts), and an army of giant bats, plus a couple of GCS, before they could reach my inner wall. If they reached my inner wall, the mayor would pull the panic lever, sealing all entrances- and trapping the invaders in the kill-zone between my two walls. It was beautiful.
EDIT: I think it was called "Dwellrim"