Istanbul's Grand Bazaar (Kapalı Çarşı, or Covered Market; map) is Turkey's largest covered market offering excellent shopping: beautiful Turkish carpets, glazed tiles and pottery, copper and brassware, apparel made of leather, cotton and wool, meerschaum pipes, alabaster bookends and ashtrays, and all sorts of other things.
In 2018 the bazaar decided that it would open for business seven days a week from 08:30am to 19:00 (7pm), and would also be open on national holidays during the same hours. The only exception is that on the first day of the Ramazan Bayramı and Kurban Bayramı religious holidayperiods, the bazaar will be closed. It will open for the remaining days of each holiday period.
Most guidebooks claim that it has 4000 shops. Because of cosolidation and replacement of shops by restaurants and other services the number is certainly lower, but you get the idea: it has lots of shops. Not all of them, by the way, are for tourists; locals shop here as well, lending a welcome dose of authenticity.
Best Shops in the Grand Bazaar:
Ethnicon/Dhoku Carpets 
Owner Memet Gureli runs EthniCon and Dhoku in Istanbul to sell some of the highest quality Turkish carpets to consumers from around the world. He is a third generation carpet salesman who has been selling in the Grand Bazaar for 45 years. As the most award-winning rug company in Turkey, EthniCon offers outstanding prices for their Turkish carpets of the highest quality and style without overcharging customers, as many carpet shops do.
Tell Dhoku/Ethnicon Carpets that "Turkey Travel Planner sent you" for best pricing, often times additional discounts, and assurance of an excellent experience because of the valued TTP recommendation!
Iznik Works Ceramics 
Iznik Works has been a trusted name in Turkish ceramics for years, located in Grand Bazaar, and featuring a vast selection of reproductions of Seljuk and Ottoman works. There are 4 locations to choose from in the Grand Bazaar so don't miss out on this shop that brings history and traditional artwork together for it's customers.
Tell Iznik Works that "Turkey Travel Planner sent you" for best pricing, often times additional discounts, and assurance of an excellent experience because of the valued TTP recommendation!
A dozen restaurants in the bazaar allow you to have lunch in the midst of your shopping.
You'll want to hone your bargaining skills before you plunge into the markets. Tips...
Beware of pickpockets and bag-slashers in the crowds.
Divan Yolu, the avenue from Sultanahmet to Beyazıt Square (the large plaza next to the Grand Bazaar) offers many interesting sights so the walk is a pleasant one.
However, the easiest way to get from Sultanahmet to the Kapalı Çarşı (and vice-versa) is via the Bağcılar tram uphill from Sultanahmet; get out at the Çarşıkapı stop.
By the way, going by taxi is not so great (and certainly not cheap) because your taxi must negotiate a tortuous route around one-way streets, pedestrian-only and tramcar-only areas.
To really see Istanbul's markets, take my Istanbul Bazaars Walking Tour from the Grand Bazaar downhill along Uzunçarşı Caddesi ("Longmarket Street") to the Rüstem Paşa Mosque and the Egyptian (Spice) Bazaar on the Golden Horn by the Galata Bridge (map).
—by Tom Brosnahan
Above, Istanbul's Grand Bazaar is a small town in itself, with miles of passageways, mosques, banks, police stations, restaurants—and 4000 shops.