In Barcelona, on the Passeig de Gràcia, there are three houses of spectacular design. Sat side-by-side in the Eixample district, the trio stand out not just for their unique façades, but because each property is in stark contrast to the next – despite having been built at roughly the same time. The story goes that, in the late 1800s, three of Barcelona’s leading architects were commissioned by different aristocratic families to redesign their homes, which meant that each designer’s creation threatened to draw eyes away from the others.

What followed was what can only be described as architectural showboating. Lluis Domènech i Montaner enlisted the help of Barcelona’s most experienced artists, creating Casa Lleó i Morera as a shining jewel with intricate ornamentation on the exterior, and stained-glass windows and mosaics on the inside. Next door, Josep Puig i Cadafalch set to work on Casa Amatller, his vision for a traditional Catalan mansion with Germanic influences. The neighbouring property was overseen by Antoni Gaudí, who brought colour to the street with Casa Batlló, a marine-inspired design reminiscent of his rainbow-hued Park Güell.

Each property is striking in its own right, but none of the architects achieved what they set out to achieve: to have their design crowned the prettiest of them all. Instead, the exact opposite happened; opinion was divided, and today the terrace is known as Illa de la Discòrdia: the block of discord.

It might not be quite the moniker the architects were hoping for, but the street at the very least cuts a pretty picture. Tucked away on my balcony in the Mandarin Oriental Barcelona, I have an excellent view of the entire terrace. Located in the former headquarters of Banco Hispano Americano, the hotel sits diagonally opposite Illa de la Discòrdia but, unlike its neighbours, is less concerned with drawing attention to itself. Indeed, by comparison the façade is understated, a sleek limestone building that you could almost stroll past unnoticed. Of course, this is the Mandarin Oriental, so any illusion of secrecy is entirely artificial – but nevertheless, when you duck into the hotel you feel as though you’ve uncovered a hidden treasure.

It’s Spanish architects Carlos Ferrater and Juan Trias de Bes we have to thank for that. When they began renovations in 2004 (the hotel opened in 2009), the designers kept the original façade relatively untouched, concentrating their efforts instead on the rest of the building, creating a vast and vibrant hotel on one of Barcelona’s busiest throughways. The allure begins with the front doors, which are offset from the street and accessed via a sloping bridge. As you wander through an ivory lightwell to the lobby beyond, the first impression is of discovering something very special.

Inside, there are 120 rooms, each the vision of Spanish interior designer Patricia Urquiola, whose eye for clean lines and a neutral colour palette, mixed with the occasional splash of Chinoiserie in a nod to the hotel’s Far East roots, makes the suites feel more like luxury apartments than hotel rooms. Champagne on ice welcomes me to my Terrace Suite, where wood-panelled walls and monochrome soft furnishings are offset by the popping citrus yellow of the armchair, vanity stool and Aqua di Parma toiletries. The majority of rooms have a balcony overlooking the Passeig de Gràcia (mine came complete with an outdoor bathtub) or a terrace leading onto the resident Mimosa garden, where a menu of Mediterranean light bites and cocktails is served.

It is one of several dining options in the hotel, the finest of all being Moments. Decorated in white and gold, the restaurant is headed up by seven Michelin-starred chef Carme Ruscalleda and her son Raül Balam, and was awarded two stars of its own for its fresh take on Catalan cuisine. The chef also steers the menu in the more informal Blanc, an all-day restaurant where a buffet is served at breakfast and an à la carte menu at lunch and dinner. The rooftop terrace TARTA serves drinks and Peruvian dishes, while nightcaps can be enjoyed in the basement Banker’s Bar, a nod to the building’s former life, with a ceiling fashioned from old security boxes.

The basement is home to the spa, which, this being a Mandarin Oriental hotel, is a highlight. There are seven treatment rooms, including a couple’s suite, where guests can enjoy a selection of spa experiences, ranging from aromatherapy massages to caviar-infused facials. There’s also a fitness centre, a hair salon and a 25m swimming pool, although those who favour a gentle dip over regimented lengths should venture to the roof terrace instead, where a sun-baked plunge pool is set against a backdrop of Barcelona’s skyline.

From here you feel both in the thick of one of Spain’s most vibrant cities and worlds away from the crowds. You need only peer over the balcony to catch sight of shoppers juggling bags, locals sipping cafe con leche in roadside cafes and queues of tourists snaking outside Casa Batlló (perhaps Gaudí was the true winner after all). Lean back on your sun lounger, however, and the bustle of Barcelona is forgotten. This, I think, is what makes the hotel so special. Cleverly designed to be so central and yet so private, the Mandarin Oriental Barcelona manages to strike the balance between city break and tranquil retreat; an inviting space to return following a day exploring the city’s sights, the majority of which are within walking distance of the hotel. It might not be the most flamboyant building on the Passeig de Gràcia, but this only serves to enhance its charm. On this side of the street, at least, it’s what’s inside that counts.

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