Cistern of Theodosius
Built 1600 years ago during the rule of Theodosius II (408-450).
The rivers of ancient Constantinople were not an efficient water supplier so
water had to be brought from outside of the city.
Also known by its Turkish name Yerebatan Sarayı (“Sunken Palace”)
About the hand, I have no idea.
Basilica Cistern, Istanbul, Türkiye