Built in the 6th century by Emperor Justinian using columns from the hippodrome and elsewhere, it lay undiscovered for some time after the Ottoman takeover. Then the Ottomans discovered some city residents could lower buckets into their basements and collect water. For years, it lay vacant until the late 20th century, when it became a tourist attraction.

All the columns are very old, and are lit up with tiny lights. This place is unbeatable for ambience.

One highlight of your visit will be seeing the overturned Medusa head blocks, which may have come from a shrine.

There are also still fish in the water. Photography Tips With its twinkling lights in the water and ancient columns, the cistern is an ideal place to take photographs.

Bring high speed film if you must use a point and shoot. Flash will not result in the best pictures. If you have the luxury of controlling the exposure, you can use slow film and your results will be less grainy. I used 800 speed film with satisfactory, if grainy, results.

If you are working without a tripod, rest your camera on the ground and use a long shutter speed to capture the ambience.

Here''s a tip to get a great overview shot of the cistern. As you are descending the staircase into the cistern, rest your camera on the steps facing out. Set up a long exposure with a high aperture to get all the details. Try 30 seconds with an aperture of 8. You will get a very atmospheric shot including the details of the vaulted ceiling. Practical Details Finding It Near the Aya Sofya, in the direction of Gulhane Park. There are clear signs marking the entrance. Hours Open 09:00-18:00 daily, except Monday (October to March : 09:00-17:00 )

There is a cafe overlooking the water, where there are sometimes concerts. You exit the cavern through a set of a stairs leading to a bookstore with some English language books.