I haven't done it on the Wish but I am sure its not much different. We did it on the Dream on embarkation day (we skipped the sail away party for it).
We checked in, took us to the locker rooms, then to our treatment room. It was a full glass window so we would see us sailing away. Side by side massage tables.
Started the massage, had us hold hands at one point, when it was over they offered some recommended products, gave us the receipt to sign/tip, and we went on our way.
I personally don't know if we will book it again. Not that it wasn't a good experience but now that I've been getting massages more often on cruises I really like massages other than swedish (not that they're bad, just I like others more), so I'll be looking into booking one of the bigger packages.