Tell me all about spa service on Navigator

[LalaCoop]

I’m thinking of saving my OBC for spa services, but have a few questions.  First, is there anything special about the spa?  Soaking tubs, steam room?  Or is it “just” a massage/treatment?  Am I good if I wait until onboard to book?  Do they do giveaways/discounts on board?  Any treatment you loved/loathed?  Thanks for you guidance!

[Clarea]

Discounts are usually best on port days.