The Buddha discusses states of extreme bliss attainable through meditation:
Secluded from sensual pleasures, secluded from unwholesome states, a bhikkhu enters and dwells in the first jhāna, which is accompanied by thought and examination, with rapture and happiness born of seclusion.
...If you could really concentrate on a metronome, it would be more blissful than a symphony. The jhāna is also a strong contender as a theory of beauty: beauty is that which is compressible but has not already been compressed.
It is related that the bodhisattva Manjusri was once standing at the gate, and seeing him, Shakyamuni Buddha called to him, "Manju, Manju, why don't you come inside the gate?"
Manjusri replied, "I don't see anything outside the gate."
When you once attain true self-realization, these barriers disappear in an instant as though they were nothing but mirages, and you will find that from the very beginning you have always been in a world where there is neither inside nor outside. That is what "gateless" means. Therefore, all koans are impassable barriers for those who are unenlightened, but for the enlightened there is no gate at all. They can come and go quite freely.
One day, as Kyogen was clearing the undergrowth, a pebble bounced off the tip of his broom and resounded against a bamboo tree. Hearing the sound, he suddenly experienced great enlightement. The first stanza of the poem he composed on this occasion is very famous:
One striking sound,
and I have forgotten all I knew.