Is the poem a riddle? Not a classic Who am I or What am I, but Where am I?
In which case, the first stanza would say something like I, the chest, went in there empty and then I went in there filled. 
Which raises the next question—the critical point of it all—in There, aka the Secret Where.
If Forrest wrote the poem as if it was a classic riddle, he might have imagined himself as the box personified and given clues accordingly. Does this hold up? 
So, if the bronze chest is speaking to you, (no, I haven’t gone ‘um die ecke’, not yet anyway), and says “Take it in the canyon down”, “it” can’t be the chest, right? Or, then again, “take it” might mean carry the chest . Different train of thought….
More wordplay? Google –How to Write a Riddle Poem, etc.
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