Deep-pocketed tourists with a yen for a view go to the Top of the Mark, while thirsty visitors of marginally lesser incomes gravitate to the Fairmont bar. That leaves the classy, low-key den in the foyer of the Big Four Restaurant at the Huntington Hotel, a short block away, for us locals. The dimly lit, oak-laden cubbyhole is cozy, adult, and quiet, although obnoxious yuppies occasionally break the spell. But then, they're not paying you any notice, are they, as you huddle over your drinks ($6.50 for a Cutty on the rocks, $8.50 for a kir) with someone special and, ahem, secret. Not so long ago, the bar's endless dark wood reeked of testosterone and old money. When a woman sets the liaison in this Nob Hill landmark these days, all that power is hers. The Big Four Restaurant is open all day, from 7 a.m. to midnight; the bar opens at 11 a.m.