Almost six million of us live in the cities and suburbs around its shores; we see it shining there, between the buildings at the end of the street; we drive across it on great soaring bridges. We are sometimes surprised to smell the sea in the breeze of evenings, or hear the fog horns before dawn. Early in the mornings, from my front porch, I can gaze at it beyond the hills, prickly with ships, holding the gleam of sunrise.

Although we may not pay it due attention, San Francisco Bay is always in our lives; it gives us our glorious setting, our air-conditioned climate.

Yet few of us have sailed as passengers upon its waters overnight, voyaging on commercial vessels across the Bay and up the rivers to inland cities.

It wasn't always so; as early as 1841 there was regular sailing launch service between San Francisco and Sacramento. In those wild decades of the Gold Rush and after, thousands of passenger boats of diverse size and description pressed up through the Delta. When the weighty WPA guidebook California was published in 1939, it noted that in Sacramento, one could still catch a boat to San Francisco every day at 6 p.m. at the M Street Wharf.

So it's good news that one can now board a cruise ship sailing San Francisco Bay and its historic "contributaries." During the autumn, the trim ships of Alaska Sightseeing/Cruise West migrate down from glacial northern waters to dabble in northern California. Two itineraries are offered: three nights over a weekend, four nights midweek.

Last spring, I signed onto the 84-passenger Spirit of Alaska for the weekend cruise.

It all worked out so nicely. My duffle bag hoisted upon my shoulder, I left my San Francisco office Friday at 4:30 p.m., took myself to Pier 40, clambered aboard the comfortable little cruise ship, and sailed away for a new perspective on local waters. Early Monday morning, after breakfast, we docked again at Pier 40, and by 9 a.m. I was back at my desk, booting up the Mac.

In the meantime, I had seen my own neighborhood from an unaccustomed vantage, slept three nights with the Bay beneath my pillow, revisited some of my favorite haunts in historic Sonoma, the Napa Valley, and Old Town Sacramento, enjoyed pleasant food and wine in congenial company, and learned some new things about the grape. And I came home with a new admiration for this Bay of mine.

Like most cities beside the sea, San Francisco is at its prettiest during the sunset hour. Spirit sailed out from the South Beach Marina and cruised north and west along the cityfront. The passengers gathered on the top deck, teeth to the brisk wet wind, to admire it all. Most of us were locals, feeling smug indeed. Lights were blinking on in the buildings piled on the hills, traffic rumbled far overhead on the bridges. In the seafood restaurants early diners leaned across candlelit tables. Pleasure boats, ferries, and tourist cruisers were slipping into their berths, the bellowing sea lions hauling out. We passed under the Golden Gate Bridge, bounced around in the Potato Patch for a few moments, then turned a 180, bound for Sacramento.

During a good dinner prepared by Chef James Marks (from Mama Donna's in Napa) we slid past Red Rock and under the Richmond/San Rafael Bridge. Mt. Tam was a black hulk against a pale turquoise sky. On this night, the northern Bay was unusually calm and glassy. At the entrance to San Pablo Strait, we admired the gingerbread lightkeep's house on East Brother Island.

When everyone else was diving into chocolate pecan torte, I was topside again, bundled in woolens, spellbound by the scene of a great urban body of water at night. All around us was a glittering collar of lights-cities, towns, piers, bridges, lighthouses, freeways, occasional freighters and tankers bound for foreign ports.

We crossed San Pablo Bay, sailed under the Carquinez bridges, brushed past Crockett and the big neon proclamation C and H Pure Cane Sugar. Then: Benicia, Martinez, and their connecting bridge. Later, when I crawled into my comfortable bunk to read, slipping by my wide window were the oil refineries, bristling with lights and flares. Sometime after I fell asleep, Spirit of Alaska dropped anchor to spend the night in the Sacramento River off Rio Vista.

By dawn next morning, the best part of the weekend was underway: the 52-mile voyage up the winding main channel of the Sacramento River to the capital. (Big ships use the Deep Water Ship Channel, several miles west, to reach the Port of Sacramento.) A few early risers were already on deck, their paws wrapped around hot coffee and tea.

The next few hours were among the most pleasurable I have experienced on a cruise ship: on a sunny spring morning, watching the Delta go by.

Years ago I had explored some of the Delta on my bicycle, and a bit of it in a kayak, but I had almost forgotten what an interesting piece of geography it is.

Before the white men came, the Delta was a great tule marsh around the confluence of the Sacramento, San Joaquin, Mokelumne, and other rivers. Back in the 1870s it was tamed into fantastically rich farmland by Chinese laborers, brought here after they had finished building the Central Pacific Railroad. With shovels and wheelbarrows, they began to shape the levees.

Today the Delta has some 1,100 miles of levees, protecting and irrigating more than half a million acres of agricultural lands. It also contains some 700 miles of waterways, from the big rivers to lazy little sloughs, and marshes and other habitat for wildlife-some 275 species, too many of them greatly endangered-and about 800 "unleveed" islands. More than 40 percent of California's runoff from snow and rain drains through the Delta-and half of that is diverted to various water projects.

Spirit's top deck was high enough for us to see over the levees to the asparagus fields and pear orchards beyond. We moved upriver slowly-wakes can damage the rock "riprap" protecting the levees-and surveyed a rural scene out of yesteryear. Along the banks stood bucolic towns with a look of the 1930s, Victorian farmhouses surrounded by poplars and palms, small marinas, an occasional drawbridge opening for our passage.

And the birds! Mallards drifted beneath the dipping branches of weeping willow; terns and cormorants fished. A black-crowned night-heron flapped along the river's edge, kingfishers swooped from tree to tree, a handsome osprey surveyed possibilities from its perch on a telephone pole.

Lunch was served al fresco, on the deck-barbecued salmon, salads. Off in the hazy distance: the snowy crest of the Sierra.

North of Clarksburg, there is a big bend in the Sacramento. Off to portside, through the trees, were the capital's cluster of downtown buildings. Then they were straight ahead off the bow, then to starboard.

Not long after, the Tower Bridge lifted to admit us, and Spirit of Alaska spent the afternoon conveniently tied up behind the Delta King in Old Town Sacramento. Passengers were offered free docent-led walking tours through the cobblestone streets and passes to the California State Railroad Museum. Shuttle buses ran them around to the Capitol Museum, Sutter's Fort, and other local historic and tourist attractions.

As for me, after the walking tour I went over to the gracious Crocker Art Museum, oldest public art museum in the West, which has exhibits as varied as its housing-a sleek new wing attached to an 1873 Italianate building lavish with tiles, marble, and tropical hardwoods. For more than two hours, I was absorbed by Dürers and Gilhooleys. The Crocker has a satisfying collection of California paintings, from the evocative 19th century landscapes of Bierstadt to the recent cityscapes of Thiebaud. And I always spend a few moments renewing my acquaintance with Charles Nahl's deliciously romantic paintings of early California flanking the grand staircase: "Sunday Morning in the Mines," and "Fandango."

As for the rest of the afternoon...well, I went to the sale at Macy's in the Downtown Plaza Mall.

Our departure from Sacramento was wonderfully dramatic, at dusk, just as floodlights illuminated the Art Deco towers of the Capitol Mall bridge. The lamps of Old Town and the glowing highrises slipped away behind us and faded into the darkness of the riverbank trees.

In Spirit's compact lounge that evening someone with the delightful name of Chenin presented a lecture and tasting of Domaine Chandon sparkling wines. She told us so many cute things. That you shouldn't age sparkling wine for long-"chill it and kill it." That champagne goes well with salsa, chips, and even Oreos. Why you should drink sparkling wine from a flute, not a wide-cup glass. When a woman should dab champagne behind her ears. What the shape of a champagne glass has to do with Marie Antoinette's left breast.

After dinner, a handful of giddy passengers gathered at the bow. The night was very black, with the Big Dipper hanging over the ship, and we were moving fast on the downstream current. Occasionally the running lights would surprise an egret roost-dozens of egrets looking, in the dark, like white paper tossed into the riparian trees. One, startled, took off and slowly flapped across the bow and downriver until the night folded around it.

If you're going... Alaska Sightseeing/Cruise West offers "California Wine Country" cruises in the fall. Contact AAA Travel Agency (our Service Directory can help you find the AAA Travel Agency nearest you,) for information and reservations; you can also get a descriptive brochure by calling the cruise line at (800) 426-7702. In 1996, the weekend cruise described here will be aboard the 84-passenger 166-foot M/V Spirit of Discovery. Prices range from $449 to $1,049 per person, double occupancy. There are a couple of single cabins aboard for $749 per person. If you book through AAA Travel Agency, you'll get a $25-per-person discount. Departures are Friday afternoons from September 27 through November 22. During the week, cruises last five days and four nights, visit more wineries, and also cruise the Carquinez Strait and Suisun Bay in daylight. Included is lunch in the dramatic Cask Room at Merryvale in St. Helena. Departures are Mondays from September 30 through November 18. Prices range from $599 to $1399 per person double occupancy, with a couple of single cabins for $999. Pier 40 is easily accessible by public transportation: BART, Muni, and Amtrak are all nearby at the foot of Market Street. For passengers flying in, Alaska Sightseeing/Cruise West provides a shuttle to and from SFO. Costuming: Dress is casual aboard, but check local weather reports before you pack. You may need everything from thick sweaters, windbreaker, hat and gloves for foggy and windy nights on deck in the Bay, to shorts and t-shirts for hot days in Sacramento. Two AAA maps will help you follow your route during the cruise: San Francisco Bay Region and Sacramento Valley Region.

At Sunday's dawn, Spirit was tied to the muddy bank of the Napa River, at a place called Cuttings Wharf, in the drizzle and fog. Our busy itinerary that day: morning at Sonoma Plaza, lunch on board, afternoon in the Napa Valley, sail at sunset.

The passengers scrambled aboard a bus, and we set off along the Carneros Highway to Sonoma. The wild mustard was blooming a dazzling yellow; red-winged blackbirds trilled from the fence posts. At Sonoma Plaza most of our group followed an ebullient guide on an entertaining walking tour of local historic sites; a few went off for "treatments" at the Sonoma Spa.

In the afternoon we drove up the Napa Valley and enjoyed private tours of two very different wineries: Schramsberg and Trefethen.

At Schramsberg, founded in 1862, delicate sparkling wines are made by the "méthode champenoise," but the main attraction turned out to be the caves, some 2.5 miles of them carved into the volcanic rock. We entered through the dewy old gardens, and ambled through cool tunnels where some three million bottles of wine are stored. We learned that a good riddler can turn 10,000 bottles an hour by hand, and that those big bubbles in young champagne are called "toad's eyes," and how to pour champagne with one hand, your thumb in the bottle punt. Deep in the mountainside, by candlelight, we tasted a bit of blanc de blancs, a touch of brut rosé, a sip of crémant demi-sec.

Down the valley at Trefethen, we stood in fields of merlot and cabernet vines, just in bud break, and listened to a discourse on viticulture-vertical trellis systems, rocky and acidic soils, icroclimates, sugar content-all the many things that go into the California wines that grace our occasions large and small.

That evening, during the Captain's Dinner, we sailed the ten miles from Cuttings Wharf down to the mouth of the Napa River, and slipped into San Pablo Bay as the last light of day faded.

There was another night of cruising through reflected city lights, along the East Bay waterfront, to our night's anchorage off the Port of Oakland. My last sight before falling asleep: the lights of San Francisco beneath the Bay Bridge.