I asked Tarn when he thought he and Zach would reach version 1.0. “Twenty years from now,” he replied. “That’s the number we talk about.” He chuckled at the prospect, adding that even when that milestone arrived, Dwarf Fortress would keep growing. “This is going to be my life’s work.”

Tarn, 33, lives in an apartment complex abutting one of the many shopping plazas that make up Silverdale, a town he calls “a strip mall.” His place has two bedrooms, the larger of which he uses for programming and which is nearly empty except for his computer desk, a framed picture of his part Manx, part Maine Coon cat, Scamps, and a fuzzy cat tree. In the living room are two gray folding tables for playing board games like Arkham Horror and Descent, and a box of Xbox 360 and PlayStation 3 games. Tarn said he seldom touches these because “most of them suck.” The only furniture in the small dining room is Scamps’s litter box.

If much of Tarn’s apartment suggests a tenant who never fully moved in, his bedroom suggests a tenant who never sets a sock outdoors. When I peeked inside, rumpled underwear, discarded boxes and books lay scattered across the carpet. A sheet of plywood, edged with black foam rubber, was wedged into the window frame and affixed there by metal clamps. Tarn wakes up around 3 p.m. every day, codes through the night and goes to bed around 6 a.m. The plywood keeps slumber-disturbing daylight out of the room, making it a chamber fit for a vampire dwarf — or at least for a computer programmer.

Tarn and Zach’s parents live on several wooded acres in nearby Bremerton, and Zach, who is 35 and between jobs, has lived with them since 2002. Zach brought over a drinking glass from the house in case I got thirsty, because Tarn owns only a couple of dishes. In the fridge were three sodas and a jug of water and nothing else. Tarn said I was welcome to anything, although the jug technically belonged to Scamps — the tap water has something in it that makes the cat refuse to drink it. Tarn consumed “maybe one glass” of water in the last three months, hydrating with soft drinks instead. “Water’s not doing it for me these days,” he said. “I know it’s bad, but the sugar goes right into programming the game. If I don’t drink soda now, I get a headache and can’t do any work.”

Near midnight one evening, after a chat with Zach about incorporating sewers into the game, Tarn settled into his coding routine, opening his C++ software and firing up a Pandora playlist of upbeat soul. (Zach, less adept at programming, contributes to the game by brainstorming ideas.) Tarn surveyed the code, arrayed before him in tiny type, and began rocking in his swivel chair so vigorously that its joints squawked. The rocking had nothing to do with the music. “It’s a tic,” he explained later. “Sometimes I don’t even notice I’m doing it. During tests at college, people would yell at me to knock it off.”

As Tarn got into the zone, his muttered profanities and grumbles about “x distances” took on a mantralike quality. Conjuring sewers, he would type out lines of code, let the software effect his changes, frown at the results, then tweak. Initially, the sewers appeared as an illogical tangle of blue gashes, but line by line, Tarn worked them into coherence.

At about 1:30 a.m., a family of hippos, represented by light gray H’s, swam into the tunnels from a nearby river. Their arrival was an unintended development born entirely of the game’s internal logic. Tarn was pleased. “The hippos like the sewers!” he said. He took a celebratory swig of Dr. Pepper and rocked back and forth.