The Cistern of Philoxenos, or Binbirdirek Cistern, is a man-made subterranean reservoir in Istanbul, situated between the Forum of Constantine and the Hippodrome of Constantinople in the Sultanahmet district. It has been restored and is now visited as a tourist attraction. The entrance is located at İmran Öktem Sokak 4. Binbirdirek Cistern is the second largest cistern in Istanbul after the Basilica Cistern.