SEMIPALATINSK TEST SITE, Kazakhstan - The road is an aged dirt track running in a line across the Central Asian steppe, past grazing cattle and horses, arriving at a hillock overlooking a parched basin.
There are no warning signs. There is no gate beside the abandoned guard shack at the remains of the fence. Only the climbing numbers on the radiation detector suggest that perhaps it would be best to turn around.
In the basin below, before much of it was vaporized, there once had been one of the more awful open-air laboratories a nation has ever made, and one of the darker secrets never kept.
Here, briefly, stood a metal tower roughly 100 feet high, ringed by sturdy objects: brick buildings, a bridge, bunkers of reinforced concrete and a park of idled tanks and aircraft, some with live animals tethered inside, set at various distances to see how they weathered what came next. Concrete observation towers were arranged at fixed distances in several directions, their instruments connected by subterranean cable to a distant command post where the experiment's masters could assess their work.
On this spot on a summer morning in 1949, Soviet scientists detonated Stalin's first atomic bomb. Over the next 40 years, in the air above the steppe and the soil of the surrounding area, scientists detonated at least 455 more.
Kazakhstan's nuclear arsenal is now gone, returned to Russia in the 1990's. But one of this sprawling country's dismal inheritances after decades of Moscow's rule is this vast poisoned zone. It is a measure of the disarray bedeviling many corners of the former Soviet Union that access to it is fully unrestricted.
If you can find your way here, you can enter at will.
The car continues on, bouncing over the washboard trail and passing the buckled remains of an observation tower nearly two miles from ground zero for the first bomb, which American intelligence officials labeled Joe One, a derivative of Stalin's first name.
Near the very center, Yuri G. Strilchuk, an employee at Kazakhstan's National Nuclear Center, which conducts limited monitoring of the radiation emanating here, leaves the car and moves forward with careful steps, taking care not to drag his feet or overturn small stones. The ground, he says, is still "hot." Flipping stones turns the hotter sides up.
The dangers vary. Experts say that short visits, with a guide and radiation detector to navigate through "cooler" areas, are not necessarily unsafe. Longer visits, or any disturbance of the soil, increase the risks.
Before Mr. Strilchuk are the ruins: scorched embankments of a vanished bridge, concrete bunkers with tops sheared away by shock waves of unimaginable force, the pond-sized hole on the spot where the tower that held Joe One stood.
Stalin regarded the work here as so vital that the atomic program's director, Igor V. Kurchatov, worried that if he failed, he would be shot. The nearby research city, now a near ghost town called Kurchatov, was not marked on maps. Its postal address was frequently changed to mislead spies. (The names included Moscow 400, Semipalatinsk 21 and Nadezhda, Russian for hope.)
Mr. Strilchuk moves forward. The sights are otherworldly.
The blasts generated such heat that the surface of the steppe was liquefied and splashed onto the surviving steel and concrete. The substance remains - a thick and dark lacquer, frozen as it oozed and dripped.
It is also underfoot. Marble-size balls of glassified soil crunch beneath Mr. Strilchuk's boots. He reads his radiation meter. Safer to stand here, he says. Not there.
Bits of life have returned around him. Grass pokes through the baked soil. Birds bank on the wind. Scattered here and there are the droppings of sheep, goats, horses and cows, which wander the test site to graze. There are signs of man as well: empty vodka bottles on the baked earth, torn bags of potato chips.
The test range is a peculiar post-Soviet legacy. In an area roughly the size of Israel, the Joe One site is just one of several places where the hundreds of bombs were detonated. Across this vast stretch, no one who wanders the range can be sure of the risks. No one who lives nearby can be sure the meat in markets did not come from animals that grazed on radioactive grass. No one knows where all of the irradiated metal has gone.
What is known is this: The site has been stripped almost bare. Scavenging gangs have yanked the thick copper cables from the ground and dismantled and carted away the parked aircraft and fighting vehicles.
Almost everything has vanished. Mr. Strilchuk recalled seeing the blast-warped barrel of an artillery piece a few years ago, jutting from a partly melted bunker. It too has disappeared - radioactive waste converted to scrap. "They take the metal and sell it," he said.
For a country that started with promise, the looting is a disappointment. In 1991, President Nursultan A. Nazarbayev declared Kazakhstan a nonnuclear zone, and by 1994 the bombs and bombers were gone. The cooperation alleviated fears of nuclear proliferation in a Muslim country and helped build relations with the West.
But Kazakhstan, a nation sapped by mismanagement and corruption, has had less success cleaning up the nuclear mess it inherited.
People as far away as Siberia have complained of symptoms from exposure. Various studies have labeled the region an environmental disaster. And the extent of pollution remains unknown, in part because Russia has not provided detailed information about the tests.
Dr. Zhenis R. Zhotabayev, the center's science director, said that to assess the range properly, create a contamination map and develop a management plan, soil samples should be taken throughout the range, one for every 10 square yards.
But because of money shortages, samples have been taken in quadrants of about 2.5 square miles. "We have to cover it kind of randomly," Dr. Zhotabayev said.
International aid has come, but not enough, and too late. Out on the range, on the once molten soil, Stalin's test range has already been picked clean.