Even in the earliest planning stages of the dome, I wanted there to be some mechanism in place that would keep the entrance to the fortress sealed against all but the most determined enemies. To that end, I drained the top layers of the volcano and constructed a hollow tower made of obsidian blocks, leading from the upper fortress into a hewn passage to the dome.
There is a side passage off the south stretch of the pillar-lined passage. Beyond this is a low-ceilinged, engraved chamber.
In the chamber are dual stairwells which descend into magma. To any visitor to Weatherwires in the past few decades, this has been a dead end. However, at the pull of a lever, the volcano can be drained again, and the magma will recede low enough on the stairwell to provide access to a curious chamber.
This chamber looks odd in Overseer because all of those open spaces are covered with steel grates. The moment the magma recedes below the level of the grates, the passage becomes accessible without having to wait for a bunch of 1/7 magma to dry.
The passage out of the chamber leads to obsidian structure within the caldera. This passage is also built out of mostly masterwork steel grates. The entire passage can be made accessible in a matter of days - and just as quickly, the volcano naturally refills when the draining is stopped.
Walking across the grates would be nerve-wracking for any non-dwarf - if any non-dwarf had crossed the passage. If anyone stands here, it has been while lava roiled and surged mere feet below them, occasionally spurting a pillar of molten rock into the air - anyone familiar with volcanoes will recognize this phenomenon. These surges ignore the steel grates - although it hasn't happened yet, it is possible for an individual, while crossing the grates, to be immolated by a blast of lava.
This is the last view the dwarves had when they crossed the grates and entered into the darkness.
Of course, if you were to look down, you should see a line of steel grates, with a lake of churning magma immediately below. Instead, this is what's rendered:
At the end of the grates is the nether-cap door, Syrupsevers. It is encrusted with obsidian, decorated with nether-cap and encircled with bands of cat's eye, light yellow diamond and goblin bone. The door (presumably the non-magma side) menaces with spikes of black-cap, reindeer leather, and cave spider silk. On the door is an image of a diamond in diorite, possibly representing the unbreakable fortitude of the dwarves. It is a priceless artifact.
It is also, unfortunately, not rendered in Stoneseer.
Just beyond Syrupsever is a ramp that leads up - if, for whatever reason, something should lodge the door open, the magma will not clog the passage. All that Syrupsever does is ensure that there is no need to wait for magma to dry for the passage to be accessible.
We've passed the magma seal and are now inside the obsidian block structure. A single tile wide staircase leads down - although it looks inaccessible, steel grates connect the top of the stairs to the rest of the chamber.
Looking down the stairs, in the interior of the structure. This view, of course, would be obstructed by a masterfully crafted steel grate.
Here we are at the base of the stairs. The passage ahead leads out of the caldera and into the tunnel system.
The passage is long, and generally surrounded by magma - the heat must be devastating.
At the end of the passage is the blessed relief of cooler air, and a small chamber. To the right is the tunnel that leads to the duke's chambers, which have been sealed off from the upper fortress. Now, they are accessible only from this point - and thus, the rest of the dome.
To the left is a doorway which leads to the top of the next stairwell.
Once more - the top of the stairwell is made accessible by masterful steel grates. According to my stocks menu, I have over 300 steel grates - and the vast majority of them are used somewhere in the fortress.
The top of the staircase, looking down. It's gonna be a long climb, but at the end is the real goal of this tour - the dome of Weatherwires.