Tsui based his design on African termite mounds:
The structure is designed to consist of 120 levels, each with its own mini-ecosystem featuring lakes, skies, hills, and rivers. In place of an air conditioning system, aerodynamic windows would help to cool the interior. Just as water from the bottom of an African termite mound cools the rest of the structure, waterfalls on the lower levels—and a giant surrounding lake—would also provide natural air conditioning (cool air rises and is warmed by bodily activity on the upper levels). And a series of mirrors at the building’s core would reflect sunlight throughout. [source]You can check out the stats here. Imagine, only $150 billion! That's just $150,000 per resident – not bad on the Bay Area real estate market. Unfortunately, the residents of San Francisco remained unconvinced:
"San Francisco has this prejudicial view of what architecture ought to be, and it's a very backward and provincial view," Tssui says. "There's a very strange, discriminatory prejudice for retaining that ancient model of San Francisco [at the turn of the century]. It’s been a huge challenge to defy that, and I've had nothing but troubles trying to create something innovative and meaningful and purposeful." [source]Tell me about it, Eugene: nothing makes me think of the words "backward," "provincial," and "discriminatory prejudice" like San Francisco.
If you've read my novel Dragonfly (and if you haven't then I hope you will), it will be plain why Mr. Tsui's proposal interests and amuses me. But let's hear it from the draft of its sequel, The King of Nightspore's Crown, in which Keftu makes his first attempt to enter the Tower of Bel:
The sun climbed to the meridian, and land was out of sight; the sun declined before my face, and darkness mantled the earth. The daystar pursued its appointed course and rose in the east again. The earth was a watery ball, the viaduct a thread stretched across its face, a path from infinity to infinity.
And then at last like a faraway giant it strode through the waves, a faded pillar against the gray-gold bowl of the sky, the axle of the ocean-wide wheel, linked to the rim-city by iron spokes. It marched toward me as the white-hot sun sank again to the sea.
No longer was I a voyeur peeping through a picture-viewer's lenses. It was there before me, the city's crown and pinnacle, the center toward which all men strained, the font from which all culture flowed. From the sea-floor to the stratosphere it rose, its weight upheld by girders that stood on the abyssal plain. Above the waves its shape was like an irregular, many-sided pyramid whose slanting faces became ever steeper as they narrowed, curving upward rather than converging upon an apex, forming a pillar like a tapering prism which, from a distance, looked like a sharp spike set to goad heaven itself.
Its smooth gray sides were gradually resolved into a mosaic of windows and hangars and terraces. A sunlit corpuscle descended upon its stratospheric crown like a spark of divine inspiration. The viaducts that converged at its broad base were so many slender spider-threads.
The rail-car crossed into the annular belt of floating crops just as the sun began to melt into the horizon. The sea-vegetables were tended by helots, but no helot lived in the Tower. They were brought over from the coasts in weekly shifts.
The belt was miles across, and dusk had fallen before the car gained the inner boundary. The Tower had by that time swollen to occlude the sky, its faces aglitter with silver diamonds, its stratospheric crown yet ablaze with the light of day.
The train was passing over the ring of pleasure gardens now. The paper lanterns were like colored fireflies visiting the floating plats.Like the Ultima, the Tower of Bel is an edifice built to house a city, featuring miniature ecosystems and supplied with piped-in sunlight. Unlike the Ultima, space elevators link the Tower's stratospheric crown with the Hanging Gardens of Narva, a toric space-palace in geostationary orbit. The Tower is located in the middle of the Tethys Sea, with its bulk partly upheld by the force of buoyancy; the ocean provides a natural cooling system, like Mr. Tsui's moat (ahem, lake), but also ensures that the riffraff of the city can be held at arm's length.
Of course, the Ultima was designed before the Tower of Bel, but I didn't know of it. Believe it or not, I even based my design on termite mounds! (The biota of Antellus are Paleozoic, so hymenopteran social insects such as ants, bees, and wasps are off-limits. So are grass, flowers, milk products, butterflies, bread, and wine.) It's kind of scary when life imitates art...