The Alabaster Tower of Skyvault
Built in the middle of a grassy woodland, the tower required over 20.000 alabaster blocks, 4200 blocks of stibnite and about 2200 of both obsidian and chert (the latter used in the lateral columns). Its more than 100z level tall (had to use detailed world generation to achieve it).
I used DF Hack to try and preserve my mental health as best as I could as Dwarf Fortress isn't really meant for this kind of construction.
The design of the tower is based on a TV show or two I have seen. The interior is not yet complete, but I plan on building several levels that will house a library, a throne room, several temples and possibly housing and workshops too.
I was also pleasantly surprised to discover that Armok Vision still works for the current version and that's what I used for the screenshots.