You need a secret code to enter Frank’s. Punch the numbers into a telephone dial pad in a phone booth outside the bar,and a concealed door swings open to reveal a classic cocktail joint that swaggers with the decadence of a 1920s Chicago speakeasy. Inside Frank\'s in the evolving Hollywood neighbourhood, Buenos Aires’ young and beautiful sip classic cocktails like the bourbon-based Old Fashioned, and house twists on vintage tipples, like the Old French Style, a dry aperitif that is a delicious, aromatic blend of single-malt whisky, orange bitters and truffle honey. Over at Isabel, meanwhile, in the ultra-cool Soho district, patrons lounge in oyster-shaped booths backed by floor-to-ceiling mirrors. This glamorous clientele sips bubbly champagne cocktails and highballs like the 1950s Puerto Rican classic, Campari Cooler. Doppelgänger, in the bohemian San Telmo quarter, celebrates 1930s Berlin. Its customers drink dry Martinis with twists of citrus peel beneath Art Deco lighting and modernist artworks. It is slightly maverick and deliciously shady; a place lifted from an inter-war-years yarn by Graham Greene. All have diverging concepts, but these bars share one major trait: they are leading lights in this wave of hip new cocktail bars. The inspiration here is the 1900 to 1960 golden age of the cocktail, when everyone from starlets of the silver screen to Chicago mobsters sipped glamorous drinks like the Aviation (a blend of gin, maraschino liqueur, crème de violette and lemon juice) and the Manhattan, which is made with whiskey, sweet vermouth and bitters. If the retro tipple is not your thing, the city also has plenty of stylish, modern cocktail bars to appeal to the contemporary cocktail drinker. Río Café in Soho is winning fame for its simple, zingy inventions, much loved by creative-industry professionals who seek tables in Río’s multi-space interior or on its funky, palm-tree-shaded terrace. They order cocktails like the Pomelo Rossi Sangria – a mix of Martini Rosso, pink grapefruit juice and fresh mint – that are simple, punchy and served in jugs for sharing. So what is driving this exciting new cocktail scene? All Argentines share a lust for the thrillingly new and creative; and the country’s economic prosperity is giving its residents the hard cash to convert cool concepts into exciting realities. The Argentine capital is also a hotspot for young North Americans and Europeans who are keen to escape the ravages of the recession at home, drawn by Buenos Aires’ repute as South America’s most glamorous city. Although this new influx of immigrants barely registers at a national level in Argentina, it is keenly felt in Buenos Aires -- particularly in its most fashionable districts, like hip Palermo Soho, upscale Recoleta and emerging San Telmo, where the majority of new expats now choose to live. In these neighbourhoods, youthful entrepreneurs with an eye on the zeitgeist are responding to shifting micro demographics. While many daring bar and dining concepts have centred around the food, designed to seduce a broader diversity of palates, others are experimenting with mixology. Inés de los Santos is a drinks designer whose inventive creations enliven drinks menus across the capital, including at Río Café. She says the secret behind these great cocktail bars is synergy.    “Río Café is inspired by Río de Janeiro, and its cocktails reflect that city’s spirit. These are light, uncomplicated drinks: breezy, fresh and cheerful – just like the city – and they match the cool, breezy style of this bar,” she said. “They are different from the complex, classic cocktails at Frank’s or Doppelgänger, which are just as successful in their own surrounds.” Head to Río Café on Wednesday or Thursday around midnight, when DJs play sets. Isabel – arguably Buenos Aires’ sexiest cocktail spot – thrives on Fridays. Frank’s (access the entrance code via Frank’s Facebook page) and Doppelgänger fill up on weekends after midnight. And if you hanker after something truly different, Prado y Neptuno is a boutique cigar and cocktail spot in the exclusive Recoleta district. Here you will find smoked-infused cocktails and daiquiris served with a splash of sweet vermouth – sacrilege to the cocktail purist. Try their magical Mai Tai; the base of Caribbean rums is poured not from a bottle, but from a tiny French-oak barrel, where it is stored for weeks and infused with rich cinnamon and vanilla flavours. From BBC travel