Tirta Empul is a Hindu temple built in the 10th century, or so our guide Marta told us. Built on top of a spring, it's water is considered holy and bathing in the waters is considered one of those 'must do' Bali experiences
There is an entrance fee of 50000K per person, you get a sarong to cover your knees.....but we skipped actually getting in the water and performing the purification rites. We arrived latter in the afternoon shortly a rain shower so it was not as crowded as some other have commented.
Definitely an interesting experience, beautiful venue, definitely worth seeing as long as it's not too crowded.
Be aware that as you exit the complex you'll have to run a long gauntlet of tourist shops, pretty much all selling the same thing, some of the shop keepers can be a little aggressive.