In the heart of the Tenderloin's grime and crime, lies a speakeasy with stiff drinks, house rules and underground passageways.

Prohibition has been over for 76 years, but San Francisco's Bourbon & Branch is still shelling out drinks like it's 1929.

The counterintuitive trend has been booming in this country lately, offering the public nostalgic trips in time to the days when drinking was hush-hush, said the bar's manager, Joel Baker. From Bourbon & Branch in San Francisco and the Violet Hour in Chicago, to the Hideout in Brooklyn, pricey cocktails that are being concocted in shadowy settings are drawing in more and more people, he said.

"Our drinks aren't cheap," he said, but Baker attests to seeing more customers in the past few months than he's seen in the three years he's been with Bourbon & Branch. "We pride ourselves in the caliber of cocktails we provide."

"People have an affection for this period of American history, and they want the mystery," Brian Sheehy, an owner of Bourbon & Branch, said.

"You'll see the master chef from a high-priced restaurant sitting in a booth next to the young couple who just got out of a show in the theater district," Baker said. "The one thing they have in common is they all enjoy finer spirits."

People come for the quality of the drinks, he said of the high-priced and alcohol-heavy cocktails, which range anywhere from $11 and up per drink.

However, there's a reason people will foot the bill for these drinks. Bourbon & Branch carries many limited production whiskeys and scotches, including a Canadian whiskey, Crown XR, which only had 7,500 cases produced, he said. There is also a rare bourbon, Glenmorangie Margaux Finish, one of 1,200 bottles in the U.S. that can be served.

"The prices are worth it for the ambiance," Ryan Tabaldi, a 22-year-old economist graduate from SF State, said. "They definitely could lower the prices, but if people are willing to pay the price, then why should they lower it?"

Tabaldi said Bourbon & Branch is a bar he'll go to every once in a while when he wants to indulge, but on the special occasions he does go, he feels justified in emptying his wallet.

A customer can order a gin and tonic for the same price as a crazy and interesting cocktail at a normal bar - the difference is that Bourbon & Branch will substitute drink-decoration with more ounces of premium alcohol, Baker added.

Baker, 31, has been bartending and working in restaurants in the city for a decade, from Café Claude in the Financial District to Aub Zam Zam in the Haight.

"America has only two real cuisines, one is BBQ, the other is cocktails," Baker said. "Prohibition killed the art of bartending in this country, and Bourbon & Branch wants to reinvent and reinvigorate the style of making cocktails."

A steady bar since the 1860s, Bourbon & Branch has remained faithful to the corner of Jones and O'Farrell Streets from the Barbary Coast days through Prohibition until now, Baker said.

The façade of Bourbon & Branch is unscathed and unmarked, with a single sign hanging from the corner of the building that reads, "Anti-Saloon League" as its single signifier of a bar.

"Considering the neighborhood, it's good to remain anonymous," Baker said while moving some bottles of whiskey around on the bar.

A patron rings the buzzer and says the secret password to the doorman, gaining access to the speakeasy. In order to obtain a password, a customer must first make a reservation via the bar's Web site, he added.

Baker was quick to point out the house rules posted throughout the establishment. They forbid the ordering of cosmopolitans, flash photography and request people to keep the noise down by enforcing a "speak easy" policy.

"You can get a cosmo anywhere," Baker said. "We get people to step outside their comfort zone."

The speakeasy offers a drink menu that has its own table of contents for the customer's ease. More than half of their drink recipes are their own, along with having homemade liqueurs and grenadine, adding to the bar's authenticity, he said.

"They actually transport you to that era," Mel Kreitz, a marketing graduate from SF State, said. "You actually feel like it's prohibition."

Kreitz said he first found out about the bar years ago and has been attracted to it ever since.

As imbibers walk in, they have their choice of staying in the main room with booths and stools, or entering through a bookcase trap door into the library room. It's located in the back of the establishment, and cocktail lessons are given against bookshelf backdrops sporadically throughout the week.

Between January 1920 and December 1933, the speakeasy was called Ipswitch. Located underground in the basement of what is now Bourbon & Branch, it served liquor illegally to San Franciscans, according to Baker.

The JJ Russels room, which was a cigar shop acting as a front for the bar during prohibition, is now a prime destination. It can be rented out for $500 a night for medium-sized events and has a secret trap door leading down to the original speakeasy.

The basement, which has floor-to-ceiling liquor cabinets and a small bar, now houses private parties. Last month, Beam Global, the makers of Jim Beam whiskey, reserved the basement for a secluded dinner, he said.

Baker said the original bar room, which was no larger than a medium-size closet, held all seven cabinets of liquor spread out on the south wall of the basement during the speakeasy days.

A sign saying "ladies" above a dark hallway to that bar's left marks a secret passageway leading customers underground across O'Farrell Street to the Garland Hotel -- it was considered to be "the ladies' exit," he said.

However, only special guests are privy to exploring the passageway, he added.

Kreitz, 33, wanted to open up a bar just like Bourbon & Branch because of the mysterious atmosphere it provides.

"If you're looking at it from a marketing scheme, it's brilliant," he said. "You gotta differentiate."

Reservations can be made at http://www.bourbonandbranch.com. To ensure a spot, reservations usually need to be made two weeks beforehand.

"There's no stone left unturned," Baker said. "It's something you need to try at least once."