This is the point of no return...

Standing in the plaza of the Mayan city of Altun Ha, shadowed by the giant Temple of the Sun God, you can almost feel the gaze of the gods. This was the ancient Mayans' Olympus: a blackened stone fortress, home to angry deities who, at one time, could be appeased only with human sacrifices. That these monuments to a strange and violent world still remain makes you wonder at the final calamity that sent the Mayan civilisation into free-fall and urged the population to leave the teeming city.

We reached Altun Ha after a half-day's boat trip up the Belize River, which meanders to the coast like a large brown snake sliding its way through the jungle. Entering the Belize River from the sea through Steamboat Creek was like being poured down a tapering funnel of mangroves.

Beyond the dark, swampish creek, the open river was far less ominous. There was life here, and, to prove it, a tarpon made a splash after taking a peek into our world. Further along the river a small boy paddled past a ceiba, or cotton tree. Mayan legend has it that ceiba roots reach down and grasp the nine levels of the underworld, while above the ground, the trunk grows up through the 13 levels of life. Ceiba branches hold up the sky - a belief that might appeal to those who see rainforests as the world's oxygen supply.

Beyond an abandoned and decaying saw-mill we entered the jungle. There we were formally announced by a jay, the brown uniformed policeman of the forest. Everything was big here, the bank lined with big-boned trees hiding big animals, the thought of which gave us a big fear. Even the leaves of the dwarf shrubs that grow on the forest floor are big. When the wind gusts through them they flap and buckle like umbrellas blown inside-out in a rainstorm.

A gang of vultures huddled round and squabbled over a recent kill. Others retreated to the trees, where they perched brooding, their enormous dark wings wrapped round themselves like seedy tar-black raincoats.

We scanned the river's edge in the hope of seeing a crocodile. According to our guide, there were plenty, but they were difficult to spot. They float motionless, low in the water, with only periscopic eyes and nostrils breaking the surface. After a few false alarms a piece of wood near the shore was caught in the boat's wake. It reluctantly came to life, churlishly flicked its tail and winked a steely eye. A fellow voyager fired off a generous burst of celluloid.

After capturing one trophy he aimed up into the jungle canopy. At first I could not see what he was photographing until a thin hairy arm lazily reached for a high branch. Then the rest of the black howler monkey, called "baboon" in Creole, swung into view from its leafy hiding place. As we watched this lone creature plot a path through the complicated map of branches and trunks, we could hear the distant roar of the rest of the troop.

The black howler, once threatened by yellow fever, now thrives all the way along this stretch of the Belize River. It shares the tree tops with thousands of richly coloured birds. It seemed they were everywhere: the kingfisher that launched itself from a calabash tree to dive-bomb a bite- sized fish; the tiny humming-bird, a scrap of sparkling velvet that hung in the air on blurred wings; and the enormous blue crane that loped along the river dipping the tips of its wings into the water.

Then it was time to pull ourselves out of the boat and make our way by dusty road to Altun Ha. After centuries of neglect, the city was rediscovered in 1957 when a Ministry of Works bulldozer tried to plough a path for a road through the dense forest and bumped with a crunch against it. By 1963 the archaeologist David Pendergast had been alerted to the discovery of jade among the ruins and started an excavation of the lost city that lasted seven years. During that dig the celebrated jade head - an effigy of the Sun God, Kinich Ahau, carved out of the translucent green rock - was pulled from the dust. It is now in a vault at the Belize Bank, and sees the light of day on rare occasions under security so tight it squeaks.

As you approach, the temples of the city rise out of the jungle like icebergs floating on a sea of green. We entered the site through the first plaza. Surrounding this are temples and administrative buildings in varying degrees of excavation. Small trees and tenacious shrubs grow between the cracks in the rocks.

Our eyes were quickly drawn beyond the first cluster of buildings to the daunting Temple of the Sun God. We climbed to the top of this towering building, admired the view and contemplated the altar, which for many had been a point of no return. Then we avoided a similar fate by descending almost vertical steps down again.

Once back on solid ground, it felt invigorating to have climbed the ancient Mayans' power-house, to have walked in the plazas where the Maya once went about their business. Returning to the straight lines, right angles and almost terminal scruffiness of Belize City, our notions of civilisation were as tangled as the jungle that drapes much of this dozily amiable country.

How to get there

No airline flies direct between the UK and Belize; most connections are via points in the United States. Journey Latin America (0181-747 3108) has flights from London on Continental via Houston for pounds 570, or American Airlines via Miami for pounds 633. Note that you have to stay overnight in the US, at your own expense, on the outbound journey.

How to get around

Public transport in Belize is slow, erratic and entertaining. Ex-US school buses operate along the main roads, charging minimal fares. Some domestic flights in light aircraft are available from the airfield in Belize City, but fares are high.

What to spend

The Belize dollar (B$), worth half the US dollar; so pounds 1

is B$3.20.

Who to ask

Belize High Commission, Harcourt House, 19a Cavendish Square, London W1M 9AD (0171-499 9728).