Some luxury hotels avoid posting their most expensive and exclusive rooms online.

Many of the rooms are available only for well-connected clientele who have heard of the rooms via word of mouth — and have the funds to pay for them.

Hotels keep their rooms unlisted for a variety of reasons, including to protect their assets and to create buzz.

How are you supposed to book a room that isn't listed on a hotel's website?

Well, the point, as reported by Bloomberg, is that you probably can't, unless you're connected enough to have heard about it by word of mouth.

That's often the case with ultra-luxurious rooms and suites that high-end hotels purposely omit from their listings. There are no photographs, no descriptions, and no prices available; to anyone who isn't in the know, it's as if they don't exist.

Hotels keep such rooms secret for a variety of reasons, whether protecting the hotel's assets or protecting the guest's identity and privacy.

Then, of course, there's the thrill of exclusivity. As The New York Times put it, hotels use these unlisted rooms "as a way to delight valued guests or generate buzz."

Read more: A 5-star boutique in Switzerland with a world-famous infinity pool no longer has to pay for advertising, thanks to Instagram

These rooms go by a variety of terms — owner's suites, partnership suites — but one thing they have in common is a hefty price tag.

Take, for example, Blue Lagoon — one of Iceland's most recognizable tourist attractions. The Retreat is a luxury hotel with 62 suites that can be booked online, some of which offer direct access to the lagoon. But tucked away within The Retreat is The Blue Lagoon Suite. There's no mention of it on The Retreat's site, but, according to Bloomberg, it goes for $10,050 a night — and requires a minimum two-night stay.

Booking details vary for these unlisted rooms. In some cases, an interested guest has to call ahead and specifically request the suite. Other hotels require that their penthouse suites be booked by email in advance, so that managers have time to vet the guest before making a decision.

Even if booking an unlisted hotel room is a bit (or a lot) out of your budget, there are still ways to customize your five-star hotel experience with some semisecret perks. That can include free Champagne or chocolate-covered strawberries and even special decorations in your room.

And hotels aren't the only businesses that build a name for some of their products — if not their entire brands — by choosing not to advertise them. Consider Goyard, a two-century-old Parisian brand.

As Business Insider's Hillary Hoffower previously reported: "Goyard's prime press strategy is silence. It forgoes any advertising, e-commerce, and celebrity endorsements. It rarely grants interviews and very occasionally makes products available to the mass market."

Clearly, in some cases, not talking about your luxury product is the best way to make people want it.