I get bored and distracted easily so I end up continually starting new fortresses.
Redpages - My first serious fort in 31.0X (although I had one earlier attempt that lasted about a year before a mysterious crash bug set in). The concept is a fort whose only entrance is in the side of a cliff, overlooking a river.
Wadedcastles v2 - This is my second attempt at building an aboveground fort made up of buildings connected by bridges sitting in a constructed lake. I never finished it due to a lapse of interest in DF
Wadedcastles - This was going to be a theme fort until poor planning, repeated goblin sieges and tantrum spirals caught up with me. I decided to start over rather than try and fix it.
Lanternsplattered - Just got bored of this one.
Booksquid the Purple Greennessess of Nudity - My first fort in the Z-axis version.