Much like the residents who return to the war-torn homes as they try to salvage what they can, Gene Forrester of A Separate Peace returns as a man to Devon School, a man from the "forest" to "capacious Greek Revival temples" that impressively line the streets. He comes to unlock the myth of Phineas in the Greek way by finding the beauty and hope in life, to rejoice in life. Gene does this by facing the two fearful sites of his past, one of which is the tree, "weary from age, enfeebled, dry." And, Gene realizes that "Nothing endures, not a tree, not love, not even a death by violence." Gene is "changed" after seeing this tree from which his rival, Phineas fell.
The other site which Gene has feared is the marble stairway on which Finny has fallen in the First Academy building outside the Assembly Hall.This is where the trial held by Brinker takes place and Gene is accused of jouncing the limb. Disturbed that Gene could have deliberately done so, Finny angrily leaves the Assembly Room and takes a terrible fall "clumsily down the whie marble stairs."
It is only after seeing again these two terrible sites that Gene can resolve his old internal conflicts and settle things in his mind. Ultimately, Gene reconciles with his conscience his envy of Phineas and the "something ignorant in his heart" that has caused him to hurt Finny. His only peace is his willingness to be aware of his deliberate evil, the same "something ignorant" that starts wars.
The Tree and the Marble Stairs.
He went to see the two places where Phineas fell, the tree and the marble flight of stairs.