General Antonyms:
* Stale
* Tiring
* Exhausting
* Monotonous
* Dull
* Boring
* Depressing
* Uninspiring
* Wearisome
Antonyms Related to Specific Contexts:
* Oppressive (weather)
* Stagnant (air)
* Musty (smell)
* Overpowering (taste)
* Dry (atmosphere)
* Uninteresting (topic)
* Uninspiring (performance)
The best antonym will depend on the specific context in which you are using the word "refreshing."