What's a word for "a thoroughly enjoyable experience"? Something like the opposite of a "trial"?
The condition or sensation induced by the experience or anticipation of what is felt to be good or desirable; a feeling of happy satisfaction or enjoyment; delight, gratification. Opposed to pain.
Something highly enjoyable; a great pleasure, delight, or gratification.
Anything in which one takes delight, or which affords delight; an object of delight; a source of great pleasure or joy.
(All from the OED.)
If you mean something that gives pleasure: Delight
a high degree of gratification : joy; also : extreme satisfaction
something that gives great pleasure
If you're talking about the state of mind: Bliss
There are also joy (which can be used in both contexts), pleasure, and felicity.
You could have a ball (sense 2).
When you're having a really hard time it can feel like a trial. When you're having a really good time it can feel like a festival.