Barbara the Fair with the Silken Hair (1970)

One day, King Yeremei decides to go on a long hike in order to consider all his areas and compile their register. A well appears on his way home, but as soon as the sovereign bent over him, he was seized by the underwater king Chudo-Yudo and demanded an unusual ransom for his release — that which is in the state of Yeremei, but which he does not know about. The tsar is forced to agree to these conditions, because he thinks that each blade of grass was taken into account in the inventory — he still does not suspect that in his absence the Queen gave birth to him an heir.