On board Colombia's last passenger train to tranquil Zipaquira

Hugh O'Shaughnessy hops on board to where a spectacular cathedral has been carved deep within an ancient Andean salt mine

Given the strife that still prevails in much of Colombia, there are lots of places not to go: the oilfields, Uraba, Barrancabermeja and many others. But that still leaves vast areas of this mountainous and beautiful land to visit in safety and with pleasure. Beginners could do much worse than to start in Bogota, on the last passenger train in the country.

The ancient narrow-gauge steam locomotive struggles, wheezing and slipping in a cloud of smoke and steam up the slight incline into Zipaquira. It finally makes it to a patch of waste ground just short of the dilapidated station and the passengers excitedly get out of the 14 carriages.

It's 11.30 on a Sunday morning and the train has taken three hours to do the 25km from Bogota. Even an idle cyclist could go faster. But, hewing to the old proverb that it is better to travel than to arrive, no one seems to be worried. At an equivalent of £6 return per head, the dads, the mums and the kids have chuffed their way through the northern suburbs of the Colombian capital and out into spectacular countryside, where fat cows graze in lush pastures and the rich have their rural hideaways - a sort of South American Hampshire but with mountains.

They have had the use of a restaurant car. The on-board band has tootled away merrily on trombone, concertina and clarinet. And they have had the benefit of experiencing the Colombia of yesteryear. As the band gets out and strikes up in the bright sun beside the train, the crew fill the tender with brackish green water from an antediluvian tank and pour quantities of lubricant on to the locomotive's moving parts. The fireman sends a few shovelfuls of coal into the firebox as families and sweethearts take pictures of one another sitting on the cow-catcher of locomotive 75, the only one still working on this line.

But Zipaquira is not just the end of the line for people who like railways and days out on a Sunday. This old colonial city shows its age and elegance in its main square where the exhausted clock of the handsome classical cathedral - designed by a friar in 1800 - shows that time stands still at 23 minutes past two.

Under the trees a photographer waits for families to plonk their children on his toy horse and have their pictures taken. Young boys in uniform doing their military service fool around like young colts. Older citizens look on from the wooden balconies of the private houses.

This is a quiet, conservative little place, far removed from the violence that lashes other parts of the country. But up the hill the city has an amazing surprise for visitors. Only 10 minutes' ride uphill from the railway line stands - or, rather, lies - the second modern cathedral it has had in recent times.

I had heard that Zipaquira had built a cathedral in the depths of its Magic Mountain. This is a gigantic deposit of salt that was laid down millions of years ago when the oceans covered South America. The oceans dried out, the salt was left to be covered over with new strata and millions of years later was then pushed up by the forces which created the Andes. The Magic Mountain has been mined since well before the Spanish conquerors came here half a millennium ago. There is enough salt left to be extracted for another 500 years.

I had never felt much desire to see it, thinking it would be some gimmicky affair, the ecclesiastical answer to Disneyland, something comparable to the modern basilica of Our Lady of Guadalupe outside Mexico City where you are borne past the image of the Virgin on a Travolator. It was with no great expectation then that I bought my ticket and queued for half an hour at the mouth of the horizontal shaft that gently sinks into the belly of the mountain.

Beyond the turnstile, a gentle, dimly lit slope some 300m long leads you down to where the guide waits in the gloom for her next party of 50 visitors and the start of the next tour. The new cathedral was opened some seven years ago to replace the original one higher up inside the mountain, which had been showing signs of cracking and collapse after 40 years of use. This one, however, has been designed to last a couple of centuries.

The first impression the visitor receives is of sobriety and restrained elegance where the architects have allowed the stupendous caverns and tunnels hollowed by the miners to tell their own message, uncluttered with fussy religious decoration.

The rock is not crystal white but a pleasant grey. If you sometimes suspect you are not surrounded by rock salt all you have to do is to lick your finger, rub it against the wall and then suck.

At the bottom of the entrance shaft the Stations of the Cross, found in all Roman Catholic churches, start. Fourteen tall Roman numerals mark the various stations, each of which has a plain cross carved in salt gently illuminated, some placed in little alcoves, others standing at the mouths of great caverns which stretch away into the gloom.

Then from a balcony we get our first sight of the cathedral's huge central nave, 72m long and 10m wide with an enormous illuminated cross the full height of the space carved into the rock over the high altar. On the left is the aisle of birth and on the left that of death.

Down a flight of steps then and, to general merriment, our guide takes a minute to explain the architecture of early churches and invites us to enter the cathedral proper through one of three entrances presided over by an angel with the quotation, "You are the salt of the earth." The first is for hardened sinners, the second for run-of-the-mill folk and the third for those who don't feel much on their consciences. Not many of us choose the third option and the crowd forces me through the first. (In a place that is very strong on symbolism, this makes me ponder.)

At the far end of the aisle of birth stands the baptistery. Running water, particularly if it is fresh water, presents problems in the salt kingdom as it dissolves the rock, so babies are christened in salt water. The guide points out that, after all, much of the New Testament was played out in and around the salty Dead Sea.

Beside it in the sacristy there stands a perfect ivory crucifix carved by Caspicara, the Indian sculptor from Ecuador who centuries ago helped to make colonial Quito the greatest centre for religious art that has existed in America.

The statuary is sparse and all the more telling for that, a modern monument here and there. In the right-hand aisle benches invite us to rest after a long walk through the bowels of the earth. Still in sparkling mood, our guide tells us that in her experience only the really wicked have to sit down at this point. Those of us who are still standing revel in divine approbation. Zipaquira, above ground and below, is a very remarkable and enthralling place.

TRAVELLER'S GUIDE

GETTING THERE

With no direct flights between the UK and Colombia, fly via Paris, Madrid or a US airport. The lowest London-Bogota fare with South American Experience (020-7976 5511; www.southamericanexperience.co.uk) for travel in April is £648 on Iberia via Madrid; from Manchester, Journey Latin America (020-8747 8315; www.journey-latinamerica.co.uk) quotes £600 on Air France via Paris. To reduce the impact on the environment, you can pay £17.80 for an "offset" from Climate Care (01865 207 000; www.climatecare.org).

GETTING AROUND

The train runs only at weekends from Bogota's La Sabana station; schedules from Turistren (00 57 1 3750 558; www.turistren.com.co). On any day, you can reach Zipaquira on frequent buses from Bogota.

VISITING THERE

The Salt Cathedral in Zipaquira (00 57 1 852 9890; www.catedraldesal.gov.co) is open Monday-Friday 9am-4.30pm and Saturday until 5pm, closed Sunday; admission 10,000 pesos (£2.50).

MORE INFORMATION

The Foreign Office warns that "Terrorism, drugs and organised crime are inextricably linked" in Colombia. Its current travel advice says "There is a serious risk of kidnapping and crime throughout most parts of the country ... Most foreign nationals are potential targets for kidnapping - backpackers as much as those working for foreign multinationals".

Colombian Consulate-General, Westcott House, 35 Portland Place, London W1B 1AE (020-7637 9893; www.colombianconsulate.co.uk).