Those centuries of exploration, colonisation and trade with South America still resonate through the city, in its architecture, the port and in its fascination with and search for perfection in chocolate – or xocolata as it is in Catalan.

Brussels and Geneva may be more associated with chocolate but surely nowhere has experimented so deeply with the outer limits of what can be done with the cocoa bean or with the final product. As with its cuisine and architecture, Barcelona has pushed chocolate to the limit.

Fargas (Carrer del Pi, 16) is perhaps the most famous of the old Barcelona chocolate and sweet shops. Its corner site in the Barri Gothic, not far from the Ramblas, is something of a shrine and the shop has a distinctly 19th century air. On the footpath outside is one of the Barcelona city marks for shops and trades of note – part of the city council’s work to reinforce the value of old family owned shops in the fabric of city life and commerce and prevent the city being overrun by chains.

Fargas is wonderful and a Willy Wonka kaleidoscope of sweets and chocolate but while historic it is hardly adventurous. For true chocolate adventure, sophistication and sheer madness there is Cacao Sampaka (Carrer Conseil de Cent 292). With all the elegance and quiet expense of a Prada shop or a Davidoff cigar bar, Sampaka offers understated sin at the shrine of chocolate.

Allow plenty of time for a visit to Sampaka. From the time the odour of chocolate permeates your senses as you step through the door and your eyes connect with the violently coloured dragees, coloured chocolates, topped with rose petals, nuts, lavender or dusted with exotic sugars and powders. The place assaults every sense.

In the rear is an elegant café for degustation of you know what. Behind the bar two vast glass vats, churned by electric paddles stir viscous baths of smooth dark bitter chocolate and lighter, sweeter chocolate. Staff in sweatshirts with a beautifully embroidered cacoa pod on the chest pour the crude-oil like 80 per cent pure chocolate into cups and offer it with wicked selections from the chocolate range – Madagascar, Venezuela, Papua New Guinea, or flavours like rose, strawberry and the bizarre yet intriguing curry or anchovy.

I opted for the bitter hot chocolate first. First taste is like that sip of a truly wonderful cabernet sauvignon, all fragrance and intensity with an edge of tannin in there somewhere. Then it seems to go on and on with a length of palate no wine could match. Liquorice, moist dark soil, a hint of jungle humus and yes, chocolate in there. An amazing sensation and one which goes immediately beyond taste to a sort of drug-like zing through your cortex. It seems barely legal.

A mango juice helped to offset what I felt likely to be the heart-attack inducing impact of the drinking chocolate. The café con leche also seemed to help through what felt like a solidifying column of warm chocolate inside me. Still carrying a buzz, I wandered back to the store thinking what good Christmas presents the beautifully packaged dragees, bonbons and other chocolates made.

So, for my colleagues back at the office some slivers of 86 per cent pure Venezuelan and some 76 per cent pure Ecuadorean and a puny 71 per cent pure version from the jungles of Papua New Guinea – a geography lesson in chocolate.

Leaving Sampaka with a sense of guilt tinged pleasure and a wallet about £60 lighter after breakfast and carrying a kilo of chocolate, I headed out into the Passeig de Gracia – Barcelona’s grandest boulevard and a celebration of the architect Antoni Gaudi.

On my last trip to Barcelona, long lines and a slightly grumpy 10-year-old prevented me seeing the inside of one of Gaudi’s most famous buildings – La Pedrera, also known as the Casa Mila, the famous block of flats on the corner of de Gracia and Carrer Provenca.

Thanks to the early rise to hit Sampaka, La Ped was uncrowded and as beautiful inside as its ridiculously wonderful melted candle exterior was. The terrace was more intimate than I had imagined. Nowhere else could you imagine smashed green glass wine bottles set into render on the top of chimneys would catch the light so beautifully. The terrace is a wonderful place to view the true Gaudi masterpiece, the Sagrada Familia to the east. You must, no matter what anyone says, climb the Sagrada Familia. It is a glorious piece of madness, as remarkable for its modernity as its scale and on a par of any of the grand cathedrals which never fail to stun in the great Spanish cities.

Times recommends

• 'New York has lost its edge'
• The UK and Ireland's 25 best Christmas events
• Chalet Chef 2010: the winners