It's a city steeped in ancient history, but trendy boutique hotels and glamorous rooftop cocktail bars have catapulted Istanbul into the 21st century, says Natalie Marchant

WALKING through the narrow streets of Istanbul’s Old Town, I’m overwhelmed by the smell of roasted chestnuts and fragrant Turkish delight.

The only city in the world to straddle two continents – Europe and Asia – Istanbul is mix of different foods, cultures and religions. It has been the capital of both Christian and Islamic empires, and is now the second city of a secular state.

The seven hills of Istanbul are peppered with mosques, yet the shopping streets of Nisantasi would not look amiss in most Western capitals.

The historic heart of Istanbul is Sultanahmet, where the domes and minarets of the Hagia Sophia dominate the city’s skyline.

Once the largest enclosed space in the world, it was originally built in the sixth century as a church to show off the wealth and power of the Christian Byzantine empire.

It then became a mosque in 1453 under the Ottoman emperor Mehmet the Conqueror, before closing its doors in the 1930s and reopening as a museum.

The main nave with its 56mhigh dome is breathtaking – not only in terms of scale and its glittering mosaics, but also for being one of the few places in the world where you can see Muslim and Christian iconography side by side.

Opposite the Hagia Sophia is the equally striking Blue Mosque, its instantly recognisable six minarets silhouetted against the sun.

Other highlights of the area include the Ottoman Topkapi Palace, the Hippodrome and the rather unusual Basilica Cistern, a Roman-built columned drain hidden under the streets.

No visit to Istanbul would be complete without a trip to the Grand Bazaar. There are 4,000 shops in 66 covered streets and alleys, selling every possible thing you can imagine. I even had to use my guidebook map to find my way out, eventually emerging with a bag stuffed full of jewellery, pomegranate tea and Turkish saffron.

Newer areas of the city can be found across the body of water known as the Golden Horn. The Beyoglu is one of Istanbul’s main business and entertainment hubs, and the best way to experience modern Istanbul is to sample its wild and hedonistic nightlife.

Hidden on the eighth storey of an apartment block on Istiklal Caddesi is the panoramic and very trendy 360 Istanbul restaurant, bar and cafe.

From the glass-fronted balcony, I look out over the Bosphorus Strait, a crucial shipping route between the Black Sea and the Sea of Marmara which divides the city between West and East, Europe and Asia.

I sip a cocktail and watch massive tankers power up the strait, past domes, minarets and old Ottoman palaces.

And this is why Istanbul is so exciting. Being one of the world’s oldest urban settlements, it’s often described as the “cradle of civilisation”, yet it’s rapidly becoming a hip and glamorous city break destination.

Like the constant flow of vessels along the Bosphorus, time here refuses to stand still.