I think "sublime" is the word that best describes diving.
I remember first learning about the notion of sublimity in junior college, when we spent a year exploring Romantic and Gothic literature. One of the hallmarks of Romantic literature is the celebration of the natural world; Gothic literature, on the other hand, revolves around the wild, the terrifying, and the uncanny. The common thread tying these two genres together is the rapturous grandeur of emotions that nature - the utmost source of sublimity - elicits in the characters and readers alike.
It's hard to think of another word that describes diving so perfectly. Close your eyes, hold your breathe, and imagine -
A world that is quiet and grey in its vastness. You float, you and a mere handful of others, in the middle of this edgeless, desolate cosmos, and then with a muted nod at each other, you slip silently beneath the waves.
And again, imagine -
The exultant freedom of being underwater, a space where you can navigate with ease one more dimension than you were created to master. A space to which you're alien, but one that embraces you wholly and intimately, immediately.
And, once more? -
This time close your eyes underwater as well. Feel your breath, feel your weightlessness, feel your vulnerability. Then open your eyes and look at your hands. Clench your fingers, release them; marvel at your human-ness and how perfectly designed you are.
And lastly, imagine, if you can -
The countless wonders and mysteries that must exist just outside the bounds of your vision and your mind.