You can understand why — were their city a little less perfectly located, were the climate anything other than unerringly benign, were the alluring parallel universe of the biggest nation in the Spanish-speaking world more than a $2 tram ride away — the average citizen of California's southernmost city might feel miffed. Irked enough, perhaps, to sink another happy-hour San Diego Sunset from the open-air bar that is not merely called Altitude — it is at an altitude of about 300ft above street level. From atop the Marriott Hotel, you can watch the day close over the Pacific.

As the sun's final scarlet flourish inflames the mountains then melts into the haze, the horizon, and — ultimately — the Pacific, consider San Diego's mild exasperation about primacy.

California is the richest state in the wealthiest nation on earth, and San Diego is among its most opulent locations. Yet the city has to cede to Los Angeles in scale and population. Poor San Diego. Yet it is, nevertheless, impressive.

The steel-and-glass skyline of downtown rises in the east. In the foreground, a big naval base, home of America's Pacific Fleet; in the background, the roasted rock that makes California such a scenic dream. In contrast, Coronado, a low-lying neck of indulgent territory, lies to the south. Beyond it, the busiest international frontier in the world: where America meets Mexico, and splashes out on a Tequila Sunrise. Northwards, a wave of beaches ripple their way up the coast, with names reverberating from the Beach Boys’ songbook. And to the west, simply the biggest ocean in the world.

For a couple of centuries after its founder Juan Rodriquez Cabrillo breezed in in 1542, California remained a backwater (gold would not be discovered in seductive quantities until 1849). But the Spanish conquerers became concerned about incursions from the Russians. So Spain dispatched a ‘sacred expedition’ from Mexico to establish roots, and a route, through California.

The man with a mission was Junípero Serra, a Franciscan friar from Mallorca, who established a Catholic settlement a few miles east of the present city centre. You can explore Serra's spartan dwelling, built around 1774, amid a complex of religious buildings that marks one end of California's original highway. This is the start of the Camino Real, the King's Highway, which runs north for 600 miles, connecting 21 missions. Each is a day's journey apart on horseback, making it ideal for a fly-ride holiday.

San Diego's global ambitions are most visible close by in Balboa Park, named after another adventurous Spaniard: Vasco Nuñez de Balboa, the first European to see the Pacific. This extravagant collection of architecture, gardens and wilderness began life as a piece of commercial opportunism. After the Panama Canal opened in 1914, the city wanted to show how the shortcut between the Atlantic and Pacific put San Diego on the map. So they launched a Panama-California Exposition here, and named the park after Balboa, who saw the world's biggest ocean from a peak in the Darie*region of present-day Panama.

San Diego has borrowed the best ideas from around the world, such as Washington DC's concept of a boulevard lined with museums, from fine art to photography — and a copy of the Alcázar gardens from Seville. More than 1,000 acres of wilderness provide the chance to get lost in the middle of America's eighth-largest city.

If it slithers, sprints, splashes or simply sits and snacks, you can probably find it here, at San Diego Zoo, nearly a century old and still one of the best in the world.

Urban landscape highlights include the William Heath Davis House, a prefabricated New England home shipped around Cape Horn and now housing a museum; and the Horton Grand Hotel, which takes you instantly back to the Thirties and includes a Chinese museum in the foyer. The other handsome redbrick structures in the Gaslamp Quarter no longer deliver prostitution and tattoos; they now house inspirational enterprises such as Le Travel Store, precisely the place to get kitted out for an adventure south of the border to Tijuana or Tierra del Fuego.

The other surprise in downtown San Diego is that you can go shopping — proper, extravagant American shopping — in the city. As out-of-town strip malls sucked the commercial life out of city centres across the US, San Diego shrewdly decided to build a first-rate mall in the middle of town.

International trade is what built San Diego, as you discover at the Maritime Museum, which celebrates the city's seagoing heritage. The star attraction is the Star of India, which was launched on the Isle of Man in 1863 to bring immigrants to America and is now the oldest ship in the world with a regular sailing schedule.

An even more impressive piece of maritime history is tied up along the waterfront. The Panama Canal opened the year the First World War broke out, but it wasn't until the year the Second World War ended that a ship was built that was too big to fit through the canal. And here it is: the aircraft carrier USS Midway.

For a decade, it was the biggest vessel in the world. It saw service in Korea, Vietnam and the first Gulf War. Since 2004, she has been one of San Diego's biggest visitor attractions, giving you the inside story on a giant war machine.

For a pleasurable boat ride from downtown then step aboard the San Diego Bay Ferry to Coronado. Greater San Diego offers a total of 33 public beaches, some of them featured in Beach Boys lyrics, but the most sought-after sands shimmer beneath the grande-dame bulk of the Hotel del Coronado, whose celebrity guests included Marilyn Monroe (who filmed Some Like it Hot here half a century ago), Bill Clinton, Madonna and Humphrey Bogart.

No charge is payable for San Diego's final treat, still in Coronado: the home of L Frank Baum, creator of The Wizard of Oz.

As you discover when you devote a couple of days to San Diego, being the second city in the most powerful state in the world's supreme nation isn't so bad after all.

GETTING THERE

Most visitors to San Diego fly into Los Angeles International Airport (LAX), but this involves a road journey down Interstate 5 to San Diego.

Getting around

All points of interest in and around the city are easily accessible on San Diego's network of trams and buses. An all-day pass is $5 (£2.85).

The San Diego Bay Ferry to Coronado departs hourly from Broadway Pier, $3.50 (£2).

Staying there

Hotel del Coronado, 1500 Orange Avenue (001 619 435 6611; www.hoteldel.com). Doubles start at $302 (£159), room only.

Seeing there

William Heath Davis House, 410 Island Street (001 619 233 4692; www.gaslampquarter.org).

Maritime Museum of San Diego, 1492 North Harbor Drive (001 619 234 9153; www.sdmaritime.com).

USS Midway, 910 North Harbor Drive (001 619 544 9600; www.midway.org); $17 (£8.90).

Eating and drinking there

Cheese Shop Deli, 627 4th Avenue (001 619 232 2303; www.cheeseshopdeli.com).

Altitude Sky Lounge, 660 K Street (001 619 446 6086; www.altitudeskybar.com).

More information

www.sandiego.org; 001 619 236 1212

PURE GOLD: San Diego’s|skyline (main); Balboa Park (top right); one of the city’s

many beaches (centre); and the city’s statue of Juan Rodriguez Cabrillo (right)

SCENIC: The Pier at Pacific Beach

PROUD: City celebrates its naval history

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