Bring with you: Swimsuit, change of clothes, flip flops that you can immerse in water, sunblock/sunscreen. If you want, your own toiletries for showering.
After a night of drinking, or just because the weather is nice...this place is an amazing day. This is also a great spot for a classy girls day.
The showers are few and far between so do not expect to try to shower there quickly.
Check out their prices online. We went on a Sunday and an all day package to just do the water baths is really well priced. Apparently their massages are fantastic, but we did not indulge.
For the water circuit, start at the top deck and follow the signs. Don't skip the cold dunk in 0 Celsius. It sounds scary, but how refreshed and alert you will feel after will make the fear worthwhile. Then head to the steam room and start all over again.
If you are in the boat, don't speak...use hushed tones. It's a quite place for reflection.
Do not skip a chance to hang out a little on the hammock swings. You will want one for your home, but take a nap.
Also if you just want to swim around for a while and chit chat, the outdoor gardens have the watercircuit there as well.
The food is a little pricy but good and wearing that wristband is a nice touch so you dont have to carry around anything.
Overall, I'd be coming back here every trip to Montreal...its really relaxing and a vacation for your mind and body.