SEATTLE — Kristen’s big-city friends are curious: What does one do, exactly, at a South Sound beach house … all … summer … long?

Well. Naturally, there is driftwood to gather. Crabs to track. Tide tables to consult. Boats to row, row, row.

“The tree frog is on the deck, and it’s the highlight of the day,” Kristen says.

It’s that simple.

And it’s that deep.

“So much of life is changing,” she says. “Activities are yearlong. There’s no downtime. Here you start to let go, get more in tune with nature. It’s kind of a lost art.”

It’s hard to imagine a better studio of rediscovery than the buoyant nautical-themed getaway where San Franciscans Kristen; her husband, Greg; and their 3- and 5-year-old daughters create family memories, and preserve family history, every unplugged summer.

Roots, as well as purpose, run deep at this woodsy waterfront retreat.

Kristen’s father came to this special spot as a boy, back when there was just a “tiny teeny cabin.” He went off to college and off to war but always came back — and always told the cabin’s owners, “If you ever want to sell …” And then, they did.

“My mom cried: ‘What are you doing?’ ” Kristen says. “We had to pump water to brush our teeth. Dad carried us three girls on his back to the outhouse.”

There’ve been a few upgrades since then: Kristen’s dad has retired next door, and the tiny teeny cabin has made way for a stunning home — with indoor plumbing! — thanks to one more family connection.

The father of one of its two architects, Peter Brachvogel of BC&J Architecture (who collaborated with BC&J’s Stella Carosso), grew up with Kristen’s dad in Aberdeen, Wa.

“All my life I had heard the names and stories from his childhood,” Brachvogel says. “It was quite a surprise to connect with Greg and Kristen at the age of 51.” (In honor of the Aberdeen High School mascot, Brachvogel dubbed this “Project Bobcat” and put the school logo on all the plans.)

Brachvogel toured the family cabin, which had grown addition by addition over the summers (“It was like walking through a time capsule,” he says) and held design meetings with Greg and Kristen on its deck.

“It was going to be really hard to tear down the cabin and re-create what we had,” Kristen says. “You just can’t do that. But I wanted the layout almost the exact same, and it kind of is. You don’t want to forget all the generations before us.”

A vision evolved: a special place to build memories. A beach house. A whimsical beach house, filled with wonder and fun. And history.

Beachy whimsy kicks in on the walk to the front door, where a silvery-gray patinaed boardwalk bends through billowy seagrass; special-ordered pressure-treated pilings from Oregon; and, of course, sand. “I love my time on the East Coast,” Greg says. “It was so relaxing to see that grass in the wind and put your feet in the hot sand. It says beach.”

Inside, paddles are incorporated into the stair railings — yes; actual paddles, 105 of them, from everyone’s go-to home-design center: Cabela’s.

A crow’s nest/office, at the lofty end of a steep ladder staircase, lets Greg work across time zones without waking anyone — and with the best view in the place. “I grew up in treehouses and forts and wanted a place where the girls could be up and look down, and Greg could crawl up and work,” Kristen says. “The higher up we went, the views just got better and better. Greg can be captain of the ship; he can see the girls on the water or on the tennis court.”

In the above-garage, 500-square-foot “bunkhouse,” Kristen’s grandmother’s 100-year-old pineapple beds gleam in new white paint, and Brachvogel created a panel system on the ceiling that replicates the interior paneling of the original cabin.

Outside the kitchen-sink windows, the sills are set at just the right height for stools. Pop open those windows, and belly right up: It’s a walk-up tiki bar, where dripping saltwater-soaker-uppers can fuel up on sundaes.

Throughout, nautical flags and lighting; marine-cleat hardware; engineered French white oak flooring with a weathered look; beach grays, whites, blues and greens; and beach themes (a “starfish bathroom” and a “seagull room”) all contribute to the summery vibe that makes this so-not-a-big-city retreat a place of relaxed simplicity, and so much more.

“You don’t realize how ‘on’ you are all the time until you step back,” Kristen says. “The importance of checking out, to be a kid again — we’re out here being kids with our own kids, being present and creating memories. It’s just nice to play with your kids.”