General:
* Exciting
* Thrilling
* Stimulating
* Interesting
* Engaging
* Extraordinary
* Remarkable
* Exceptional
* Uncommon
* Unique
* Novel
* Original
* Intriguing
* Fascinating
* Captivating
More specific:
* Adventurous (for experiences)
* Spectacular (for sights)
* Magnificent (for beauty)
* Profound (for thoughts or meaning)
* Inspiring (for emotions)
* Exhilarating (for feeling)
* Sublime (for beauty or awe)
* Ethereal (for beauty or otherworldliness)
* Exceptional (for quality)
* Magnificent (for grandiosity)
* Extraordinary (for being beyond the ordinary)
* Unforgettable (for lasting impact)
The best antonym will depend on the specific context in which "mundane" is used.