Sultanahmet
Face Hagia Sophia. We'll spin clockwise to get the lay of the land, winding up back here. Behind Hagia Sophia, not visible from here, are the Topkapi Palace grounds, which also house the Istanbul Archaeological Museum. To reach the main palace entry, you'd walk along the front of Hagia Sophia, then turn left and walk along the side of the church until you ran into the Imperial Gate.
Turn 90 degrees to the right. The long building with the different-sized domes is the Haseki Sultan Bath. Just to the right of that, at the other end of the lively park, is the famous Blue Mosque. Farther to the right, you'll see a street running straight away from Hagia Sophia (along the side of the Blue Mosque), leading to the long, narrow Byzantine square called the Hippodrome (the green-domed pavilion you can see through the trees marks the near end of the Hippodrome—where we'll finish this walk). Spinning to the right, notice the street with the tram tracks. This is Divan Yolu, the main thoroughfare through Sultanahmet. Istanbul's most central TI is between Divan Yolu and the Hippodrome. As the trams rumble past, notice the dramatic boomerang-shaped swoop made by the tram tracks as they pass Hagia Sophia. Since Istanbul's Old Town tram has only one line, it's remarkably user-friendly.
On the opposite side of the tracks from where you're standing, notice the tall brick-and-stone tower. To the left of this is an ancient mileage marker. If you were to go around the tower to the right, you'd find the low-profile entrance to the impressive Underground Cistern (in the red-and-white brick building).


▲▲▲Hagia Sophia (Aya Sofya)—It's been called the greatest house of worship in the Christian and Muslim worlds: Hagia Sophia (eye-ah soh-fee-yah), the Great Church of Constantinople. Built by the Byzantine Emperor Justinian in 537 A.D. on the grandest scale possible, it was later converted into a mosque by the conquering Ottomans, and now serves as Istanbul's most impressive museum. Hagia Sophia remains the high point of Byzantine architecture. Inside, restoration work attempts to do justice to the Christian and Islamic elements that meld peacefully under Hagia Sophia's soaring arches.
 Hours, Location: , covers entire museum; Tue-Sun 9:00-18:30 (until 16:30 off-season), closed Mon, temporary exhibits and upper galleries close 30 min earlier. Hagia Sophia is located in the heart of the Old Town at Sultanahmet Meydanı (tel. 0212/528-4500).
▲▲▲Blue Mosque (Sultanahmet Camii)—Officially named for its patron, but nicknamed for the cool hues of the mosaics that decorate its interior, the Blue Mosque was Sultan Ahmet I's 17th-century answer to Hagia Sophia. Its six minarets rivaled the mosque in Mecca, and beautiful tiles from the İznik school fill the interior with exquisite floral motifs.
The tombs of Ahmet I and his wife Kösem Sultan are nearby.
Cost, Hours, Location: Free, generally open daily one hour after sunrise until one hour before sunset, closed to visitors five times a day for prayer, Sultanahmet Meydanı. (s3)
 

Your Guide to Istanbul.