Someone told me that you have to make advance reservations for the Ice Bar and that it's very difficult to get into. Is this true? If so, how do you make the reservations? I didn't see that as one of the options on the website.

Yes, it is true. The Ice Bar is limited on the number of people allowed in at any given time. If you can't make reservations on line then you would want to make them immediately on the first day of your cruise.