This is another of my favorites. I nearly tear up a little when I read it. This is a very powerful poem and is about the closest written words that illustrates the folly of attempting to describe kensho.
There's a story of Su Tung-p'o where he challenged a Zen master. A deal was struck since there was not place to sit, Su Tung could use the master as a chair. If Su Tung lost this deal/bet, then he had to relinquish his jade belt to the master. All Su Tung had to do was answer a single question.
The question: "In the Heart Sutra, it says form is emptiness, emptiness is form. If you use me as a chair, you are attached to form. If you don't use me for a chair, how do you explain this emptiness?"
Su Tung studied the problem for a long time. Traveled a bit. Eventually became lost. He then let his horse walk without guidance. The horse led him to a beautiful scene. He came into view of a waterfall. Listening to the sounds of the waterfall, he became enlightened.
To commemorate the moment, he wrote this poem:
The roaring waterfall
is the Buddha's golden mouth.
The mountains in the distance
are his pure luminous body.
How many thousands of poems
have flowed through me tonight!
And tomorrow I won't be able to
to repeat even one word.
~ Su Tung-p'o