The main underground cisterns, also called Yerebatan Sarayi (which translates as "Sunken Palace") is Istanbul's best hidden secret. It was constructed during the reign of Constantine I in the 4th century to serve as a well and a fishing hole for the locals.
Try to find the Medusa head at the basement of one of the columns!!
Located just at the right of Hagia Sophia as you go out...
Fondest memory: Yerebatan Caddesi, Sultanahmet
Telephone: +90-212 522 12 59
Open Hours: Open 09:00-18:00 daily, except Monday (October to March : 09:00-17:00 )
Walking in there was almost surreal.
There are hoards of people selling carpets in Istanbul... one carpet seller gave us directions to it... escorted us to the door... I said 'Thanks'.
We went in for about 2 hours... had some coffee... we go out... and he was waiting for us there, asking us to go see carpets.
Favorite thing: Visit Yerebatan Sarayi, a Byzantine cistern. Right in the middle of the city, opposite the Blue Mosque, you go down the stairs into the coolness and serenity of this place.