What I got in my email said it had to be in their “hotel store.”
Hotel Credits
Hotel Credits are exclusive to Princess Future Cruise Packages and allow you to save on hotel rooms found in the Princess Promotions hotel store. This booking engine includes tens of thousands of hotels around the world, including some of your favorite resort and island locations. Your Hotel Credits expire in 24 months, giving you plenty of time to find your next exciting destination.
Stay Certificates
Your package includes a 7-night Stay Certificate that can be used to reserve accommodations, at thousands of top-rated hotels and resorts around the world. You can combine your Stay Certificate as a pre- or post-stay with your cruise or use it for an entirely separate vacation. Like your cruise, you must complete your stay within 24 months of purchasing your package.