Vineyards, castles and coastlines: the California drive you didn't expect

From renowned wineries and quirky towns to thermal springs and even a medieval castle, Highway 128 is the dream road trip through California's leading wine regions. Starting about two hours' drive north of San Francisco, the "Wine Road" hits the highlights of the Napa and Sonoma valleys before a final stretch following wild coastline to Mendocino village perched high on ocean bluffs. Here's how to make the most of this hidden gem among California's highways.

The historic rural gateway town to Napa-Sonoma is cute on the outside with good food and wine on the inside. We find farm-to-table freshness in everything from simple café fare to fine cuisine, and sip acclaimed fruit-infused aperitifs at fancy bistro L'Apero les Trois, and taste dozens of California's best honeys at premium producer The Hive. But the star of the show is Winters' award-winning winery Berryessa Gap, where over gold-medal petite syrah paired with homemade paella, owner Corinne Martinez explains why locals want 128 officially renamed "America's Wine Highway". "There's nowhere else in the world where you can find the diversity of grapes, wine styles and microclimates than on this [232-kilometre-long] highway," she says.

The next day Corinne's words ring in my ears when the waiter at Napa institution Mustards Grill hands me the longest wine list I've ever seen - well over 100 varietals mostly from Napa and Sonoma printed on a single laminated poster-sized sheet aptly entitled "Way Too Many Wines". The Napa Valley is best known for high quality cabernet sauvignon. But the terroir supports so many other equally stunning wines, like the premium white we're handed on arrival at Beringer Vineyards. Founded in 1876, Beringer is Napa's longest continuously operating winery, producing more than 30 different wines. "If cabernet is the king of Napa's grapes, then chardonnay is the queen," quips our guide as we follow him past flowering gardens and into the estate's Victorian-era "Rhine House" mansion to be treated to Beringer's best drops. Later, in the quaint rural town of Calistoga, we stop sipping and start soaking in Napa's other famous liquid: the warm waters of its numerous natural thermal springs, which fill all three swimming pools at our retro boutique motel Dr Wilkinson's Backyard Resort & Mineral Springs.

In 1972, Silver Oak Cellars' single-varietal cabernet turned Napa upside down, deliberately defying the valley's then-blanket adherence to multi-varietal Bordeaux-style wines and becoming an instant hit. Buyers queued out the door, driving Silver Oak cabernet to cult status and cementing cabernet as the grape synonymous with Napa. "We stuck to our guns," recounts Silver Oak veteran Tom Walsh while pouring me a truly divine $200-a-bottle-plus cabernet. "Now our motto is 'life is a cabernet'."

Idiosyncratic wineries seem to be a thing in Napa, none more so than Castello di Amorosa. The enormous, medieval-style Tuscan castle appears like a mirage as we round a bend in the highway. Complete with moat, working drawbridge, 107 rooms and multiple wine tasting venues, the $US40 million "castle of love" is a top Napa attraction. Today we join the regular throng of wide-eyed visitors wandering the creation of fourth-generation Napa vintner Dario Sattui, one that took 15 years and more than a million ancient stone blocks, imported from Europe, to build.

But the surprises aren't over - as to reach Sterling Vineyards we must take a gondola ride high over the valley. It's the world's only winery with aerial access. We alight at its gleaming white Mediterranean-inspired hilltop facility and are indulged with premium wines served on the terrace with expansive Napa Valley views.

Hands down the best way to see the Alexander Valley in Napa's neighbouring Sonoma County. On a perfect blue-sky day, we cruise past sun-kissed vineyards with Getaway Adventures and drop in at leading wineries. It is utterly idyllic. On the deck of Robert Young Estate I gaze at vineyard vistas sipping one of the best sauvignon blancs I've ever tasted; at Zialena we lunch al fresco drinking estate-grown wines made from the vineyards flanking our table. It's an excellent way to sample some of Sonoma County's 66 varietals, thanks to the region's plethora of soils.

Don't be fooled by Geyserville's rusticity. The Wild West town in the heart of Sonoma houses sophisticated wine stores, tasting rooms and legendary restaurant Catelli's, run by celebrity chef Domenica Catelli who's worked for A-listers Oprah Winfrey, Julia Roberts and John Travolta.

Part film set, part resort, The Francis Ford Coppola Winery near Geyserville is another one-off. Built by the director famous for The Godfather and Apocalypse Now, the winery resembles a Gothic-style mansion incongruously flanked by two enormous swimming pools. Inside we pore over the extensive display of Coppola's genuine movie memorabilia, witness production of the director's eponymous wines and dine on Italian cuisine on a shady terrace overlooking the vines. Then it's onto 128's final stretch through Mendocino County, passing the US branch of prestige French champagne house Louis Roederer, the 150-year-old heirloom apple tree farm of Gowan's famous apple cider, and soaring redwood forests until the Pacific Ocean suddenly appears on the horizon.

I'm utterly charmed by this mystical seaside village perched atop craggy bluffs. The quaintest of Victorian-era cottages line the streets, many creatively adorned by the numerous artisans who live here. Today fog rolls in off the sea making everything even more moody.

We hire kayaks from Catch A Canoe, walking distance from our hotel Stanford Inn, and paddle down Big River's stunning canyon where sea otters frolic and fur seals bask in close range.

Lunch is fresh daily-catch at Noyo Fish Company, dinner a French affair at Mendocino's best restaurant Café Beaujolais.Then we rally for one last adventure: riding the rattling historic 'Skunk' Train through redwood forests to Glen Blair Bar, an open-air barn festooned in fairy lights with live music, cocktails and marshmallows to toast over an open fire. Our late-night soiree is unique and unexpected, a fitting finish to a road trip filled with surprises.

The writer was a guest of Visit California