Four Seasons Hotel and Resorts
Arguably the most beautiful hotel on this list, the Four Seasons in Florence was once the Palazzo della Gherardesca and many of the hotel’s most striking features date back to the 15th century. A short walk from the Duomo, this hotel is set in immaculate gardens and the walls of the hotel's chapel (now a reading room) were painted by Flemish Mannerist artist Jan van der Straet.
Some of the most exceptional interiors can be found in the $20,000-a-night Royal Suite, which contains an original 18th century ceramic floor by Ignazio Chiaiese and Venetian glass chandeliers.
Arguably, the Four Seasons is as much a museum as a hotel, and the seven-year renovation to restore two former palaces to their Renaissance glory was overseen by the Italian government department responsible for the maintenance of historical art and architecture.
The hotel spa is another highlight, with 10 luxurious treatment rooms and products made by the Officina Profumo-Farmaceutica di Santa Maria Novella, where monks have mixed potions from Tuscan flora and fauna since the 13th century.
Double rooms are available from $460.
Starwood Hotels and Resorts
This opulent hotel, located just across the street from the embattled Greek Parliament, offers guests breathtaking views of the Parthenon and the Acropolis — a 20-minute walk away.
Opened in 1874, the Grand Bretagne remains a favorite with American tourists. Notable guests who have stayed over the years include Winston Churchill, Joan Collins, Jacques Chirac, and Jean Paul Gaultier.
The Grand Bretagne offers everything a VIP would expect, from a vast marble lobby stuffed with neo-Baroque furniture to a rooftop pool with views over Mount Lycabettus.
The grandest of the hotel's 321 guest rooms is the 400-square-meter Royal Suite, complete with a 16-person dining room, butler, wine cellar, and private gym.
Standard rooms at the Grand Bretagne will set you back around $360 per night.
Built in 1870, this former residence of the Count of Valença is set on a hill in the wealthy Lisbon neighborhood of Lapa, overlooking the Portuguese capital.
The palace became a hotel in 1992, and its 109 rooms are divided between the historic palace itself, the Garden Wing, and the Villa Lapa, which opened in 2002 and offers a modern alternative to the ornate décor of the older buildings.
Guests are made up of glamorous Brazilian jetsetters, the obligatory wealthy Americans, and a variety of European diplomats and business types. Paul McCartney, Rod Stewart, Bono, and Cher have stayed here, adding a smattering of music royalty to the mix.
Large gardens boast a range of water features, including a pond, waterfall, streams, and a heated swimming pool.
Mandarin Oriental Hotel Group
Since it opened in November 2009, Barcelona's Mandarin Oriental has established itself as one of the city's foremost luxury destinations. Located on Barcelona's most upmarket shopping street, the Passeig de Gracia, this hotel was once the Circulo Ecuestre, a member's club for the super rich. It was also once a bank.
Indeed, the hotel bar (unimaginatively named the Banker's Bar) has a ceiling constructed entirely of safety deposit boxes in a nod to its previous function. Guests can also enjoy award-winning martinis until the early hours after dining at the Michelin-starred Moments restaurant, which specializes in Catalan cuisine.
This 98-room hotel offers a roof terrace, complete with dipping pool, and double rooms start at $450 per night.
The Ritz London
Home of the most famous afternoon tea in the world, London's Ritz first opened its doors in 1906 and has remained a benchmark for luxury ever since.
Located at 150 Piccadilly, the Ritz is the most palatial of London's luxury hotels, and its pastel-hued bedrooms are adorned with 24-carat gold leaf and Louis XVI furniture.
The hotel's Swiss founder, Cesar Ritz, intended this landmark to encapsulate the comfort of a French chateau with the grandeur of a palace. The hundreds of tourists who descend on the hotel's Palm Court each day for tea spend a few hours masquerading as modern-day royalty, as they are served jam and scones from silver platters by immaculately dressed waiting staff.
In a city crammed with some of the world's finest hotels, The Ritz is still the most famous. It has managed to stay true to Cesar Ritz's vision more than a century later, under new owners Sir David and Sir Frederick Barclay who undertook a huge refurbishment project in 1995 to restore the hotel to its original glory.
Rooms at The Ritz start at $590 per night.