(CNN) — You just checked in at the front desk of your hotel and are making your way up the elevator to your room.
Unbeknownst to you, there are people checking into their rooms in the very same building, but they're checking into an entirely different hotel.
How can that be? It's part of the growing hotel-within-a-hotel trend that's popping up at select properties across North America.
Aimed at a luxury-oriented, privacy-seeking clientele, these hotels-within-hotels are generally located on a specific floor or floors of an existing property and have their own entrance, their own staff and heightened services and amenities.
These hidden properties don't typically display signage and are rarely advertised, so you could well be staying at the same location and not even know the other hotel exists.
The Flagler Club is a 25-room boutique hotel discretely located within The Breakers, the renowned Palm Beach, Florida, resort.
It opened in late 2015 on the sixth and seventh floors of the property, following a $5 million renovation.
"The hotel-within-a-hotel strategy is used to create something more upscale, with higher levels of service refinement," explains Tricia Taylor, senior vice president and general manager of The Breakers.
"Hotels with thousands of guestrooms want to create an additional product offering within, that is smaller in scale to feel more intimate and personalized to guests," she says.
Staying at a hotel-within-a-hotel is not to be confused with staying on the club or concierge level of an upscale property, although the concept is similar.
"Concierge floors and club levels are found in chain hotels and primarily focus on inclusive food and drink," says Taylor. "Many hotels sell access passes to the concierge floor, or use it to reward loyal customers with upgrades.
"In essence, the concierge floor becomes a VIP perk, and its guestrooms could be in a dedicated area or spread throughout a hotel; they are typically the same design as all of the hotel's guestrooms," she says. In contrast, the Flagler Club's rooms, service and amenities are different from those The Breakers' main hotel offers.
"Nothing is replicated, not even the staff," says Taylor.
So where are these elite hotels-within hotels? Here are a few properties worth reserving:
The Breakers is an iconic Florida beachfront resort dating to 1896, and its guest registry over the years includes names like J.P. Morgan and Andrew Carnegie.
Had the recently opened Flagler Club been around inside The Breakers back in the day, you surely would have found them enjoying its stylish digs and plentiful perks, like complimentary fully stocked mini-bar, exclusive use of the chauffer-driven Tesla house car and the dedicated staff there to wait on guests hand and foot.
From $950 a night.
Vegas is at the forefront of the hotel-within-a-hotel trend, and this retreat on the top floor of the Monte Carlo casino is just one of the secret hotels-within-a-hotel in the MGM Resorts collection.
Its 51 rooms are decidedly larger than those in the main hotel, and the long list of amenities includes private check-in, walk-in chromatherapy rain showers, complimentary airport limo pickup and free clothes pressing and shoe shining.
Best of all, Hotel 32 is one of the more affordable hotels-within-a-hotel you'll come across.
From $150 a night.
Canyon Suites, Arizona's only Forbes Five-Star/AAA Five Diamond hotel, is located at the foot of Camelback Mountain within the 250 acres of the itself-spectacular Phoenician resort.
Guests can hang out in one of the Canyon Suites' 60 rooms and suites or in one of the cabanas at the private infinity pool.
They'll also have access to a daily wine tasting with a resident sommelier, a personal Canyon Ambassador to assist them with requests, plush bedding and bowls and other perks for their pets.
Therapeutic Turndown service -- a bath prepared with a variety of soothing salts -- caps off a day at Canyon Suites.
From $484 a night.
This 343-room hotel within the Royalton Riviera Cancun takes exclusivity to the next level by restricting it to visitors over the age of 18.
Hideaway guests enjoy access to all of the main resort's restaurants, bars, activities and fitness facilities, but when they want more privacy, they can retreat to this adults-only haven.
Complimentary extras like weekly champagne and chocolate parties, in-room aromatherapy, 24-hour concierge service and personalized beach bags are available to guests.
From $166 a night.
There's already a Nobu Hotel -- a partnership between chef Nobu Matsuhisa, Robert De Niro and film producer Meir Teper -- located within Caesar's Palace in Las Vegas.
Now another one is set to open October 1 inside Miami's iconic Eden Roc Miami Beach.
When it makes its eagerly anticipated debut, the Nobu will offer not only the same stunning oceanfront views and Morris Lapidus design aesthetic as the Eden Rock, but feature its own signature Nobu restaurant, two pools, spa and fitness facilities and more than 70,000 square feet of event space.
Rates still to be determined.