How do you book spa treatments or specialty dining?

You can book these once you are aboard the cruise ship. Simply press the ‘concierge or spa’ button on your room phone. Some cruise lines, Princess for example, will allow you to make reservations online in your trip planner before your cruise.
Spa treatments are usually very expensive aboard a cruise ship. Like, $120 per one-hour massage, plus you’ll need to tip on top of that.
There are usually several small restaurants on aboard your cruise ship that you can dine at for an extra fee, usually about $20 to $30 per person. You’ll have to book these in advance, by calling the concierge when you first get on the ship.
The food at these specialty restaurants is usually 4-star, so if you’re a big foodie it’s definitely worth it.