Haghia Sofia a.k.a the church of holy wisdom. More than 1,400 years old, a testament to the 6th century Byzantine Capital. In 15th Century, the Ottoman converted it into a mosque. Has spectacular patterned mosaic ceilings.
Blue mosque, the most famous landmark built between ( 1609-1616). Personally I find it a bit over-rated but worth visiting. Tour guide is not necessary to visit this place. Interesting light and sound show in the evening.
The interior of Blue Mosque.
The bridge spanning the Bosphorus, the straits separating Asia and Europe, which join the Black Sea and the Sea of Marmara. Cruising Bosphorus straits is one of the must-to-do trips in Istanbul . Usually half day tour.
Shopping frenzy at Grand Bazaar. Everywhere goods tumble out of shops onto the pavement. Lots and lots of jewellery, leather products, souvenir items, imitation goods, textile etc. Bargain is a must. Dont be tempted by their persuasive skills.
Entrace to the Topkapi Palace. The principal Palace of Sultan Mehmet II, a big compound with enormous pavilions and courtyards. Dont miss the Harem, the section where sultans' wives and concubines lived. At it height, the Harem used to accommodate 1000 concubines. The tour guide told me that all the concubines were not turkish but from the countries conquered during the Ottoman empire. Can be on guided tour or as an option, visitors can also rent a listening device in order to have their own tour. Dont forget to visit the Treasury where all the gifts and jewellery of the Sultans are kept. The biggest diamond in the world is on display too.