The Bullitt Center opens its net-zero energy self to the public today, showing off everything from its composting toilets to its smart brain that runs the energy system.

Coinciding with Earth Day, the same celebration that Bullitt Center director Denis Hayes actually started, the open house for downtown Seattle’s center offers the nation its most sustainable office building to date.

At over 52,000 sq ft and six stories tall, the center took Living Building Challenge codes to new proportions. Going net zero energy on a structure that size gets more difficult, harvesting enough rainwater for that many people more challenging and handling waste on site for that many tenants more cumbersome. But Bullitt plans to do it and all in the public eye.

The $18.5 million project—it works out to about $355 per square foot, slightly more than other Class-A commercial space in the city—is already 80 percent leased. And with a life expectancy of 250 years, the price tag is worth it (if all the claims hold true).

Key features of the center include its ability to go net zero on energy use, with a 14,3000 sq ft solar array that hangs over the top of the building and 26 geothermal wells that drop 400 ft for ground-source heating and cooling. With 226 cloudy days a year in Seattle, net zero is quite the feat here.

With those cloudy days comes rainwater, which the center will harvest with a 56,000-gallon underground cistern. If officials finally give the okay, Bullitt won’t even need to hook to the city’s water system, treating all drinking water onsite and then using filtering systems for gray water use.

The center features a “brain,” designed to handle all the lighting and heating needs, even opening and closing windows—in the dead of night, if needed—to optimize the center’s systems.

All waste—that is where those clever composting toilets come in handy—gets handled on site; the timber-frame skeleton was sourced locally; the site revives a previously asphalt-covered location; and building materials were toxin free.

With all the fanfare that has surrounded this exciting project, the next stage allows us to eat some pudding. And see if the proof is actually there.

Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He has also written for TIME, Popular Mechanics, Popular Science and more. You can follow him on Twitter at @tdnewcomb or visit his website here.