So, I embarked on a glacial volcano, pretty cool place, marked as Joyous Wilds (not that it matters much on a glacier). I embarked once after accidentally hitting "Play Now," so I went back and reclaimed, which is why there is a second wagon. Anyway, looks like a pretty cool volcano, and my dwarves conveniently started right on its rim.
So, I figure I'll go see where the lava is. I'm going down Z-levels, when suddenly:
It goes through the caverns? That's kinda weird, but I guess it could happen, since normally the tube goes down to the magma sea. So, I continue my search for the lava, when I find a bit more than I bargained for:
Below that is hidden, so I have no idea what's going to happen when I unpause. If it hasn't opened up the circus, it's possible that I could actually play this if the magma fills normally. This would actually be pretty cool, since I could just wall off the open part in the caverns and embark there.
And for anyone who asks, I only put in one cavern layer since I never use the other two, so they are just extra processing I don't care about.
Anyway, I'd love to upload this to the map site, but I can't remember the address. If someone could link it I'll get the .zip I made up asap.
UPDATE: I unpaused, and it looks like it just ends at the bottom of the sea. So, the magma sea is filling it in, no FPS issues, no circus (though there is one, for later possibly). As a side note, when I was looking for a site, I was thinking about how funny it would be if I happened to find a glitched site.
Another note, I generated 4096 years of history to see all the different possible engravings, so we'll see how that goes.
UPDATE 2: It looks like the caverns are devoid of mud, which may be problematic, though there is a lake, so I can make some mud. Luckily the space before the volcano tube is considered outside, so there is an ice wall between the lake and a fall into the magma sea.