Let's get this out of the way: it's probably never going to happen.

William Kaven Architecture's proposed design for the old 14-acre US Post Office site in the Pearl District adds 5 million square feet of retail, office, and residential spaces spread across multiple buildings. With two central towers anchoring the site, it would transform nearby Union Station into a true regional transportation hub, accommodating, say, the Hyperloop or another bullet train design.

But the most visually striking feature would be this crazy skybridge:

"The two tallest central towers, one of which would exceed 970 vertical feet, would be interlinked by a glass-enclosed botanical bridge spanning 236 feet across the North Park Blocks some 680 feet in the air, providing dramatic aerial views of the entire city," says the firm's press release.

The firm's partner and cofounder Daniel Kaven, who recently wrote an impassioned op-ed arguing for big thinking in development for the Daily Journal of Commerce, says this is exactly the thing we need to weather the city's growing pains.

"The size and scale of this development opportunity—being in the middle of downtown next to our transportation hub—demands a bold building," he writes in an email. "Portland will experience enormous growth in the next 50 to 100 years and density will be key to managing congestion. Portland must be ready for this level of density and we need to plan ahead for it. This is just the beginning."

"Only one building in Portland has been built since 1984 over 500 feet," he continues, alluding to the US Bancorp building, aka Big Pink, which was completed in 1983. "The proposed building itself, which would be the tallest, not counting supplementary towers and antennas, on the West Coast would tremendously add to the skyline."

So maybe it won't happen. But what if, man?