Stepping into the shadow, there's initially more to smell than there is to see. Burnt almonds, pineapples and mangoes give a cloying edge to the humid air. Along the arcade shafts of light stream among the stalls. Great glass jars catch the glare and reveal their homemade sweets. Pyramids of shaved coconut climb towards the heavy lids. And as the afternoon promenade begins, ageing voices call out their rhyming pitches: "Dulce de coco para los locos!", "Dulce de piña para las niñas!" (Coconut sweets for the crazy, pineapple sweets for the girls).
The Portal de los Dulces, one of Cartagena's favourite meeting points, has changed little in the last 100 years; the characters are just where Gabriel Garcia Marquez left them. It was in the shadow of this arcade that his epic of unrequited passion, Love in the Time of Cholera, begins. Dr Juvenal Urbino rushes to the Portal to examine the corpse of his friend Jeremiah, a 60-year-old who had poisoned himself to escape old age.
It is also the spot chosen by Jaime Garcia Marquez, the Nobel laureate's younger brother, to begin a very personal tour, both of Cartagena and his favourite novel. Jaime, a civil engineer, is an altogether lighter presence than his brother. "For me Cartagena is the laziness, the happiness," he says with a sweep of his hand that takes in the languid scene of late afternoon. "But for my brother beyond this happiness there is a great melancholy. The happiness, I believe, is the Caribbean, the melancholy is from him."
The great Latin American novelist is everywhere in this walled city and his ochre-coloured modernist house takes pride of place on the seafront, even though these days he spends most of his time in Mexico City. As we walk through the alleys of the old town past the cathedral and the colourful balconies, the narrative is pure magical realism - the style perfected by his brother. Anecdotes are crowded with friends past and present and seem to move from real events to fiction and back again, trailing the characters behind them.
The pace of life here is dictated by the climate, as Nikodemus, an old merchant seaman, tried to explain. "The temperature in Cartagena... is hot."
This is more precise than it may seem. Sometimes it rains, sometimes it doesn't. It is always hot. Leaving the Plaza de los Coches - where more than a million Africans were sold into slavery - Jaime tells me that the tale of love and suffering amid a cholera epidemic was actually a reworked version of their mother's life story. "My mother was the only girl in the family. Then along comes this man from the telegraph company. But her father didn't want the telegraph man to marry his only daughter and so forbade them from meeting. What my grandfather didn't know was that the telegraph man also played violin at the church, so the couple saw each other every week. When her father found out he sent her away. Every town she went to she would contact him through the telegraph. Finally she found a priest whom she convinced that her telegraphic suitor was the love of her life and he agreed to marry them." For anyone still unsure how the story ends, the name of Luisa Santiaga's suitor was Gabriel Eliquio Garcia Marquez.
We are searching, with no great hurry, for the house of the novel's heroine, Fermina Daza. Or rather, we are looking for the house where the girl who once inspired thoughts of Fermina lived.
We find it at 37-18 Calle Dom Benito. The shaded square where her ardent suitor, Florentino would pen his letters to her has been updated with some dubious concrete benches and raised flower beds, but the painted wooden balconies are still there. At the house itself there is little sign of life. It's easy to imagine that the doors and windows are shut tight against the heat of the day, while the residents take a siesta.
By now we are deep in San Diego, a confusing tangle of streets huddled inside the historical walled city. Settled by the Spanish in 1533, the fortifications that surround the old town are testament to its role both as staging post for the conquest of Latin America and treasure chest for the loot. Today, that greedy and violent history is still apparent in one of the most beautiful cities on the continent. The worn façades of convents, cathedrals and noble houses line the narrow streets, while terracotta tiles and grand colonial domes crowd the skyline. Courtyards filled with tropical plants can be glimpsed through wooden doorways. Antique cannonballs are routinely found in the grass outside the walls and workmen speak of sealed chambers in its restored buildings. Little wonder this is known as the "city of hidden rooms".
The grandest of its many convents was the Santa Clara, a sprawling complex that looks over the fortifications and out to sea. It was here that Gabriel Garcia Marquez, then a young reporter, witnessed the emptying of the burial crypts as the crumbling convent was converted to a luxury hotel. The 200-year-old remains of a young girl, Sierva Maria de Todos los Angeles, with 22m of red hair, inspired him to write Of Love and Other Demons.
Today, the hotel offers sweet relief from the heat and humidity. The life of an 18th-century Marquis is easy enough to imagine from the deep wicker chairs, fanned by the breeze from the fountain, watching toucans hop from leaf to branch. The exquisite chapel is now a meeting room and the relics of the past form the beautiful decor of its cloistered French restaurant. The clientele are almost all European, but everywhere else there are reminders of the city's past in the people that now live there. A few look European, a few Indian and some African, but almost everybody is a mixture.
The initial draw of Cartagena was its natural harbour, 10 miles wide and three miles long. The Spanish adventurer Pedro de Heredia arrived early in the 16th century. Heredia, a serial duellist, fled here from Spain. He tortured the locals into revealing their burial sites, then he and his men looted all the ceremonial gold. The grave robber was duly rewarded with the title Marquis. Today he stares down from bronze statues in the plazas, and is celebrated as the founder of Cartagena.
By now the city has spilled far beyond the fortress walls and many of the wealthier Cartagenans are crowded onto the thin finger of landbetween* * the harbour and the sea, the Bocagrande. Rising out of the warm water like a graphic equaliser, its uneven tower blocks compete with each other like children intent on proving who's tallest.
Our literary tour is winding down and as we pass the modern art museum, Jaime recalls a drunken night when a young Gabo and friends stumbled across a painting by a local artist of a clown's face. The only problem was that the work of art was on a restaurant door. After haggling they persuaded the owner to sell them the door. To celebrate the group went to the brothels of working-class Getsemani. When they awoke, it was gone.
Getsemani is still the focal point for the city's nightlife and a strip of clubs on the waterfront offers everything from salsa to heavy rock. The crowds start to arrive after 11pm and keep coming long after midnight. Inside, the drink of choice, as everywhere in Colombia, is aguardiente, served by the bottle with ice. Girls dance in football shirts with an effortless sway of the hips.
Waking to the heat of another day in the tropics, thoughts inevitably turn to the sea. But Cartagena's beauty is in its architecture, not its beaches, whose greyish-brown sand is home to murky water, squadrons of plastic bags and the wooden canoes of fisherman. The latter supply the fish and seafood that form the basis of every meal, from street food to the pressed linen and luxury of the Club de Pesca - arguably the city's finest restaurant, and certainly its most beautiful.
Locals, meanwhile, speak in excited tones of Tayrona, a four-hour drive out of Cartagena. As you head north, the mud flat beaches of the city give way to lush wetlands, where storks patrol the water lilies. The road, only a few inches above the swamp, continues like this along the coast as far as Santa Marta, the first of the Spanish-settled cities. After three hours, the Sierra Nevada rises out of the Caribbean and up to a snow-capped peak, far out of sight above the cloud line.
Leaving Santa Marta, the road climbs into the Parque Tayrona, once home to a Pre-Colombian civilisation and now one of the country's most beautiful reserves. Where the main road ends the rainforest begins; flowers of paradise peek out from the dense foliage. The first sign of the the sea comes with the pale mauve crabs scuttling in the undergrowth before the trail ends in a sand dune.
Los Eco-Cabinas, at Cañaveral, are among only a handful of permanent structures inside the park. With wooden walkways and natural materials they offer shelter with minimal intrusion on the environment. Accommodation is in thatched huts teetering on the granite hills overlooking the shoreline. The shuttered windows complete a full circle around the raised bedroom of the huts and the view moves from thick leaves over the smooth rocks, onto the white sand driven backwards by the roaring waves of the Caribbean Sea.
Strong tides and powerful breaks mean swimming is not advisable on the longer of these wild beaches but a short horse-ride from the lodge, through a forest alive with giant lizards, spider monkeys and butterflies, paradise gets even better. Trotting out of the trees into a campsite in Arrefices, the park offers yet more dramatic coastline. Here the sandy path leads you onto a beach where vines unroll a carpet of trumpet-shaped purple flowers stretching halfway to the water's edge. Ten minutes' walk to the east, through a coconut copse, we come across a cove where the palms lean right over the calmer surf and a rusting shipwreck sits astride the reef a few hundred yards from the shore.
It reminds me of one of Nikodemus's stories about a fishing trip out beyond Cartagena. Returning after dark in a dinghy they lose their course and hit the submerged wall that the Spanish built along the seabed to close the mouth of the Bocagrande to pirates and invaders. Stranded in the moonlight they are attacked by blood-sucking bats. In the chaos the women make to swim for shore until they are told that schools of barracuda and sharks are in the water. Eventually the boat escapes its perch on the wall and the exhausted group paddle for shore with their hands.
Like everything else I've heard since I got here, the story is sinister, enchanting and hard to believe. Perhaps, in this town, so dominated by its most famous householder, the old sailor agrees with Gabo's adage that "Life is not how you live it, it's how you remember it."
The low-cost carrier Air Madrid (00 34 902 51 52 51; www.airmadrid.com) flies direct to Cartagena from Madrid. Or you can fly to Bogota via Paris with Air France (0870 142 4343; www.airfrance.co.uk) or Iberia (0870 609 0500; www.iberia.com) via Madrid. The national carrier Avianca (0845 838 7941; www.avianca.co.uk) flies from there to Cartagena.
To reduce the impact on the environment, you can buy an "offset" from Climate Care (01865 207 000; www.climatecare.org). The environmental cost of a return flight from London to Cartagena, in economy class, is £17.20. The money is used to fund sustainable energy and reforestation projects.
Hotel Santa Clara, Calle del Torno Barrio San Diego, Cartagena (00 57 5 664 6070; www.hotelsantaclara.com). Doubles start at US$255 (£150),
Eco cabins, Cañaveral, Parque Nacional Tayrona. Cabins sleeping three people start at 62,000 pesos (£14), room only. Luxury cabins can be booked through Gema Tours (00 57 5 660 2499; www.gematours.com).
Cartagena Museum of Modern Art, Plaza de San Pedro Claver (00 57 5 66 01 957; www.cartagenadeindias.com.co/moderno.htm); entry 500 pesos (10p).
Parque Nacional Tayrona (00 57 5 243 1634; www.parquesnacionales.gov.co).
EATING & DRINKING THERE
Restaurante Club de Pesca, Cartagena (00 57 5 660 5863; www.clubdepesca.com).
The Foreign and Commonwealth Office (0845 850 2829; www.fco.gov.uk) advises there is a "continuing high threat from domestic terrorist groups in Colombia. There is a serious risk of kidnapping and crime. (It) advises against all travel to southern parts of Meta department and to the Sierra Nevada de Santa Marta (including the 'Lost City')."
Colombian Embassy: 020-7637 9893; www.colombianconsulate.co.uk
Colombia Tourism: 00 57 1 212 6315; www.turismocolombia.comReuse content