Istanbul Bazaars
In Istanbul's old city are two famous markets, each with a distinctive character, and each worth a visit. Some entrances to each can be hard to find, but both are easily accessible by public transport and reasonably signposted.

entrance to the Grand Bazaar
The Grand Bazaar
Over a quarter of a million visitors pass through this complex of 3000 small shops every day. It was begun in 1455/1456, before Istanbul's 1483 defeat at the hands of the Ottomans, and has grown into an amazing monument in its own right, and one of the oldest and largest covered markets in the world, extending over 61 streets. Over the centuries it has been rebuilt, suffered fire damage, been extended and changed shape. The result is a quirky interior with different 'zones' or 'quarters' selling different kinds of things in distinct areas.

The Grand Bazaar, Istanbul
It's as remarkable for its architecture as for its wares. Gold is a typical Turkish wedding gifts, and the bazaar is lined with wonderful gold shops where you can purchase all kinds of jewellery. Handbags, jewelry, shawls, ceramics and all those kinds of things line the market.
An English website is available
here.
Personally, I much preferred the Spice Bazaar. Known locally as the Egyptian bazaar instead, it contains the foodstuffs of the market world. A 10-minute walk from the Grand Bazaar, it is still a hotspot for tourists, but you'll also find yourself among the general Istanbul public doing weekly shopping there.
The Spice Bazaar
From the very entrance you're rushed into a purposeful throng in this busy, L-shaped market place.

Spice Bazaar, Istanbul
Great slabs of Turkish delight tempt you into the different shops, and friendly proprietors may be nice enough to cut you off bits to try (with impressive huge knives). There is, of course, the stereotypical stuff, clear and sweet, but the variety is amazing. If you're prepared to pay a little more then your sweet comes embellished with pomegranate seeds, chocolate crisps, hazelnuts and pistachios. Dried fruits themselves are stacked in boxes outside the small booths.

Wares on show in the spice bazaar
Saffron is one of the top tourist souvenirs, but you need to be careful what you buy. Small boxes of real Persian saffron remains expensive
Prices do vary between stalls, so it's worth looking around and deciding where best to spend your money. Much larger packs of local saffron are available very cheaply, but have relatively little taste and so are more useful for decoration / texture purposes. Another local speciality is Sumak, a spice mix used to marinate meats. Haggling can be an option, as some kindness in the exchange might help round the figures off a little.

Sumak
There are fabulous teas to choose from too. Dried lemon and apple peels, rosebuds, jasmine heads (quite expensive but delicious), and incredible blends to deal with all health and wellbeing issues as well as being generally tasty: they'll scoop you just as much as you want into a bag, ready for you to take a taste of the Orient home.

Rose, mixed, lemon and jasmine teas
The shops all have these amazing vacuum machines which vacuum pack all your dried good so that they comply with the export rules. Vacuum-packed spices and teas are one thing, but vacuum-packed Turkish delight is a little more sticky to unpack. There are customs limits on what you can take home, so it's worth checking your country's rules in advance.
The odd stall also sells objects such as coffee pots and shawls, but the primary business is definitely food.
Down the side of the market is a further long row of stalls, selling olive oils and olive, with dozens of varieties on offer. It's an olive-lover's paradise! Prices are very reasonable, especially if you ask around a bit, and they will happily convert Turkish Lira into US Dollars if you ask.
There are signs to both bazaars along the road, but it helps if you can read any Turkish. This is the one city I've visited, however, where official tourist police cars patrol the area and will stop to check that you are okay and know where you are going. This is very reassuring.
You should allow a good few hours to go around the two markets, and possibly some time to browse and return so that you don't impulse buy too much. Even if you're not purchasing things, it's worth going just for the atmosphere.