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Until I visited Halcyon House, I’d never walked into a start-up incubator and felt underdressed. I’d also never, upon meeting an entrepreneur for the first time, been promptly handed a sanitary pad.

But then, Halcyon isn’t your average incubator. For one thing, there’s the house’s history. The mansion, on Georgetown’s Prospect Street NW, was built in 1787 by Benjamin Stoddert, the first U.S. Secretary of the Navy; its gardens were designed by Pierre L’Enfant, the architect of historic D.C. In 1900, it was purchased by Mark Twain‘s eccentric nephew Albert Clemens, who apparently believed that he would live forever if he continually rebuilt the house, so he subdivided rooms into uninhabitably tiny ones and installed stairways to nowhere. The house was restored to a more logical form in the late 20th century, and bought in 2011 by Sachiko Kuno and Ryuji Ueno, who had earned a fortune in pharmaceuticals and started the S&R Foundation, which runs the incubator.

Then there’s the structure of the incubator. This isn’t the standard rent-a-desk arrangement. Instead, the entrepreneurs live at the house through a fellowship program. Each receives a spacious one-bedroom apartment with a kitchenette—-there’s a shared kitchen in the main house for their use—-and a $10,000 stipend for living expenses. After the residency, the fellows complete a four-month post-residency while still working out of Halcyon, then spend six months operating out of the WeWork coworking spaces.

Finally, there’s the work the entrepreneurs undertake. You won’t find any dating apps or car-sharing services at Halcyon. Each project has a social mission. S&R doesn’t take an equity stake in projects as tech investors typically do because the goal, according to S&R Chief Operating Officer Kate Goodall, is to launch initiatives with a social good and “help catalyze Washington, D.C. as the place for social entrepreneurs.”

I meet Goodall in one of Halcyon’s conference rooms, with a long wood table, elegantly carved wood chairs, a fireplace, and a gilded painting of a young girl holding a doll. (This is where I begin to feel underdressed, in the button-down and jeans that comprise the typical dress code in start-ups.) “There’s something definitive about D.C. that is not Silicon Valley,” Goodall explains. “It’s not about creating the next Angry Birds.”

Halcyon solicits pro-bono support from private companies to assist the entrepreneurs. Deloitte consults the fellows free of charge, Sage Communications does P.R., Tandem Legal Group provides legal advice, and foundations and individuals donate the stipends to the particular entrepreneurs they want to support. Halcyon also doesn’t have to pay rent, since S&R’s founders own the mansion, allowing operating costs to remain manageable.

That doesn’t mean life is spare at Halcyon. The gardens, on the roof of a portion of the ground floor with an expansive view over the Potomac River to Rosslyn, are ready-made for a wedding ceremony, complete with a trellis. (“The only thing I don’t like about my job is people calling me begging to do weddings and events here,” Goodall says.) There’s an outdoor pool, a conference room overlooking the river that hosts dinner parties of up to 40 people, a light-filled library stocked with board games, and workspace all over. The fellows’ furnished one-bedroom apartments, with ample seating and bedroom study areas, would rent for well over $2,000 a month. (Goodall avoids using the word “apartment.” “Technically,” she says, “we can’t call it an apartment because of zoning, because then we’d be a bordello.”)

The main workspace is the most modern room in the building, with a vaulted ceiling, sloped stone walls, and exposed beams. There, I encounter a few of the fellows—-and the sanitary pads.

Diana Sierra, a Halcyon fellow whose project aims to redress educational limitations imposed on girls in the developing world by providing them with affordable menstrual products to which they currently lack access, hands me one by way of introduction. It’s purple, with instructions printed on the outside and a Bounty paper towel stuffed inside. My surprised reaction, mercifully, is not the most awkward response she’s gotten. “A guy from Deloitte thought it was a beer koozie,” she says.

This is not the type of project that’s likely to be funded by the private market. When Sierra applied to Halcyon, she was “at a low point,” running out of money and energy. The Halcyon housing and stipend allow her to work without financial worry, for a time at least. The space also provides much-needed company. “Sometimes being a social entrepreneur is a lonely road,” she says. “Your friends think you’re nuts for quitting your job. So it’s nice to be with other nuts people.”

These people include Matt Fischer, who’s developing a product to predict when a child is about to have an asthma attack; Heather Sewell, who’s creating an online newspaper platform for kids; and Olivier Kamanda, who’s working on a system to help news consumers find social impact opportunities related to the stories they read.

“The stress is really the killer,” Kamanda says of the usual obstacle to social entrepreneurship. “It impedes our progress when you’re worrying about how to pay your mortgage and take care of your family.”

Halcyon House may be huge, at more than 30,000 square feet, but the incubator program is small: With just eight apartments, Halcyon accepts up to eight fellows, twice a year. This is the inaugural class of fellows. If the programs’s successful, Goodall says S&R might try to franchise it out or otherwise expand it to other sites.

Then again, she notes, “Not everyone has an 18th-century mansion.”

Photo by Aaron Wiener