Hotel dining rooms by definition are places to decompress, where travellers wan from jetlag know they will not have to wrestle with fricasseed lamb cheeks or cheeky waiters. But the restaurants of Istanbul's grand hotels aren't just for wimps. In the late 19th century, the Tokatlıyan Hotel, which catered dinner parties for the palace, was the hottest seat in town. More recently, and as more and more five-stars begin to open their doors, hotels have become stand-alone centres of glamour and culinary innovation, designed not to stop guests from going out, but to draw the city in.

In its heyday the Tokatlıyan had but one rival - the Pera Palas around the corner. The Pera Palas catered to a diplomatic clientele as well as being the terminus for the Orient Express. It was here that Agatha Christie penned the start of her Murder on the Orient Express, before moving to a seaside mansion up the Bosphorus owned by the hotel's then owner. This does not explain why she had Poirot dine at the Tokatlıyan (where he has great difficulty keeping his moustache out of the soup) before setting out on that fateful journey.

He should have come to Agatha, the flagship of the recently reopened Pera Palace, where one of the signature dishes - a potage of vine leaves - comes in an eminently sippable teacup. Chef Maximilian Thomas is a long-time resident of Istanbul, and although the dish sounds like artsy fusion, it is attractive and tasty and just the sort of intelligent adaptation of ingredients that go to make up a new Istanbul cuisine.

At its best the menu at Agatha presents familiar Turkish ingredients in interesting contexts and is not afraid to borrow from abroad. It might seem an odd thing to say, but there is respect for texture. It's not just that the grouper (or lagos - a fine Mediterranean fish) was properly springy but that I still remember the milk-marinated lamb I had once had at a banquet cooked by Chef Thomae which was firm but not tough - something kebab houses do well, but large hotels almost never achieve. Agatha boasts a menu dégustation which changes every month and is a strong believer in set menus. On the other hand, we preferred the bolder choices of ordering à la carte.

Agatha inhabits a purpose-built room which is more sedate than the porphyry- and marble-clad public rooms upstairs or the empire-style old dining room which is now the dedicated banqueting hall. But if the Pera Palace has gone through a top-to-toe makeover, this is as nothing compared to the transformation of the Divan Hotel, a familiar Istanbul landmark which has been torn down and rebuilt. In the process the hotel has changed nationality - where once it was a bit of modernist Americana, the exterior now sports Moorish brown and beige stripes. It is not an oriental fantasy. The architect, Thierry Despont, is after all a Frenchman based in deepest Tribeca. Certainly what lifts the Divan's game are the extravagant glass chandeliers in the lobby, a lotus assembled from enormous hand-blown petals and the hanging glass sculptures - a firework of exploding tubes - in the high-ceilinged, ultra-sophisticated restaurant, the Divan Lokanta.