It’s “The Rime of the Ancient Mariner”:
It is an ancient Mariner,
And he stoppeth one of three.
`By thy long beard and glittering eye,
Now wherefore stopp’st thou me ?
The Bridegroom’s doors are opened wide,
And I am next of kin ;
The guests are met, the feast is set :
May’st hear the merry din.’
He holds him with his skinny hand,
`There was a ship,’ quoth he.
`Hold off ! unhand me, grey-beard loon !’
Eftsoons his hand dropt he.
I had to memorize this one for detention in high school. I think the version I memorized was only 28 stanzas, though. It helped that I hardly understood a word of it. I was 16.