From the outside, the Basilica Cistern (pictured above) doesn’t look very exciting — especially compared to other dramatic historical sites in the Sultanahmet district of Istanbul — but it’s pretty neat on the inside. You enter the modest building, buy your ticket (10 TL) and immediately descend down a steep flight of stairs to see the oldest surviving water storage facility in Istanbul.

My first thought was they sure don’t make water storage facilities like they used to. My second thought was that I don’t think I have ever been in a modern cistern and maybe they do look like this. But I doubt it. Built by Emperor Justinian in 532, the architecture includes vaulted ceilings and Corinthian columns.

There are also two mysterious Medusa heads — no one seems to know the origin. Adding to the mystique is that one is one is on its side and the other is upside down (pictured right).

It’s dark and damp down in the Basilica Cistern, as well as a good 15 degrees cooler, making it a welcome respite from the strong Istanbul sun and an excellent place to hide out for 20-30 minutes. (If you have asthma, you might want to plan for an even shorter stay.)

I was surprised to see that there were lots of fish swimming around. If you’re having dinner in the Sultanahmet and your waiter is trying to impress you by saying how local their fish is, ask him where they get it. If he says the Basilica Cistern instead of the Bosphorous or the Sea of Mamara, run!