What is the climax in the most dangerous game? is it when he swims back to the chateau? why is that?

The climax of a story is where the conflict or problem is
resolved.  When Rainsford swims back to the chateau, the problem has not been resolved. 
Zaroff is still hunting him, and he still has to survive.  The climax comes when Zaroff
is surprised by Rainsford in his bedroom. Even though Zaroff tells him that he
(Rainsford) has won the game, Rainsford says "I am still a beast at bay" (pg 11) That is
an idiom that means he is still being hunted. He challenges Zaroff, and Zaroff says "One
of us is to furnish a repast(meal) for the hounds.  The other will sleep in an excellent
bed." (pg 11)  Zaroff then says, "On Guard" which is what is said before a fencing or
sword fight.  The Resolution or Denoument of the story is very short.  It just says that
Rainsford slept in the bed.  That means he won the fight, and Zaroff furnished a repast
for the hounds.