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.

Originally used as a water supply for Constantinople to keep its residents watered during war times when the city was under seige. It seemed to be forgotten until about 1547 when it was rediscovered by Petrus Gyllius. The Basilica Cistern (named after the Stoa Basilica that it was originally built underneath) is now one of Istanbul's most fascinating sights, and also one of the more popular.

The huge underground cistern is almost 140m long, doubling the length of the Hagia Sophia, whilst the width of 65m is comparable aswell.

As you descend from the street level you can peer through the darkness, only lit by atmospheric spotlights, just adding to the mystery and tension apparent in the building. A wooden walkway leads you beneath the magnificent domes and through the pillars topped with Byzantium Corinthian capitals.

With the obligatory coin throwing dispensed with, I made my way past the 28 rows of columns the cistern encompasses. While most of the 8m high columns are identical, there are a few that beg to differ. The most prominent of these can be found in the far left corner.

After reconditioning in the 1980's where about 8 feet of mud was removed and the walkway built. Two columns that sat upon bases depicting Medusa heads. One lies sideways, the other upside down, as legend states that if viewed the right way up, you would turn to stone. A talking point of any visit.

I left thinking what a fantastic acoustic it would be for a concert venue, and found that there is a small stage jutting out over the water where concerts are held on occaision. If this is the case then I would beg you not to pass up the opportunity, not only to see an ancient treasure of Istanbul, but to add to the sensual experience with live music.

The cistern is, indeed, atmospheric in the extreme. Entering a non-descript building on Yerebatan Street, just across from Aya Sofya, we had descended into a vast underground space. It's an impressive engineering feat, considering that it was created almost 1500 years ago. Twelve rows of columns, with 28 columns per row, stretch across the length of the vast chamber. The bases of the columns lie in the shallow, motionless water and are artistically lit so that the columns and their reflections march endlessly into the shadowed recesses. The air in the cistern is still and cool, almost dank but with no hint of decay. Spidery strains of classical violin music echo off distant walls. The effect is of profound mystery and stillness.

Of course, the original purpose of this romantic place was completely practical. It was built during the reign of Justinian (527-565), who began a great program of civic construction and restoration after the Nika revolt, a riot in the Hippodrome which spread into a full-scale revolt, destroying much of Constantinople. A plentiful water supply city was of paramount importance to the walled city, which endured seige after seige by successive waves of invaders before ultimately falling in 1453.

During the first century of Ottoman rule, knowledge of the cistern seems to have been lost. It was, oddly enough, a Frenchman, one Pierre Gilles, who rediscovered the cistern while looking for remains of the basilica for which it was named. He noticed that the local people drew water and even fished from certain wells, and descended by torchlight into the cistern with a local guide.

During the 1980's the Turkish government set about restoring the cistern. Fifty thousand tons of mud were removed, the columns were cleaned, and a platform was built so that vistors could walk through various portions of the cistern. Today, this restored cistern is universally regarded as one of the most romantic and fascinating places in the old city.

Twice I was admonished by Istanbul residents to "Go see the cistern - you must not miss it!" In particular, I was advised to look for the "Medusa heads," stone faces lying sideways and upside down, each supporting a column. The origin and purpose of these heads is unknown, though it is said they were probably pilfered from some other building when the cistern was constructed. One informant explained their peculiar sideways and upside down placement to me thus: "If you looked at the face when it was right side up, you would turn to stone! But you can look at the reflection in the water, which is right side up, and you will be okay."

It goes by the name of Yerebatan Saray which means underground palace. The vaulted roof of the cistern is supported by 336 columns!! The water is very clean down here, and although they told us we'd be able to see fish, there were none. I don't think it would add anything. There are pathways that were built so that you can walk through to the end, where an enigma awaits you, and to this day, no one knows why 2 of the columns have Medusa's head all but upright. Her face is almost completely green, and it's not nausea. She's covered with algae, and for good reason as she's been down here for quite a while

. A janitor is present, patiently swabbing the floors and steps so that no one breaks their neck.

The cistern is about 1500 years old, and I imagined how our drinking water at the Pamphylia Hotel continued to come from this source. It's fairly dark down here and humid, so you'll need a flash for your pictures, and even then, they are not all that clear. There is a good luck column here as well, into which you stick your thumb and turn it 360 degrees. If wet when removed, good luck will befall you. Well Chuck and I are waiting for signs of luck since November of 2000.

There is a small shop by the exit stairs which serves cappuccino and other refreshments. They also allotted part of the foreground to tables and chairs. I didn't see anyone availing themselves of this service, and I can't imagine anyone wanting to really sit down and make a bad hair day worse! It is a construction of phenomenal proportion however, and cannot be missed.