For those of us who are familiar with SimCity 2000 and various other mentionings of Arcologies, This challenge should be fun.
An Arcology is a self contained and self sustainable habitat. In essence, it will be a large dwarf made building which contains living, farming, power, trading, and industrial facilities. The dwarves cannot go outside of it, aside from the construction phase.
Your arcology must be built above ground. In fact, it must be supported 1 z-level above the ground. It must be self sustainable, with farming facilities, water pumps (for the farms, of course.) and power systems to power the pumps. It must have a suitable habitat area with bedrooms and a dining area. It may also have a trading area with an airlock of some sort for wagons. It must be realistically supported. No cheats may be used in it's construction.
Your dwarves may start with a suitable amount of provisions and seeds inside of it. However, after they are sealed in, the only resource that may come in or out of the Arcology is water.
Bonus points if..
It's built over something dangerous, such as magma, a chasm, or a cave lake (A cave lake would allow you easy access to water for your farming facility).
It contains facilities that allow for sustained industrial production, such as an animal breeding area for bone crafts to sell.
It has extra creative features.
It can survive for more than 10 years with no casualties or major malfunctions.
Get building.
[ April 01, 2008: Message edited by: exoleet ]