Dr. Fyodorov says visitors are already at risk of poisoning. He claims a major leak is inevitable, and will affect millions of Muscovites living within a few miles.

For years, the authorities refused to admit there was anything buried underneath this ground. But recently, a warning sign did go up. Still, there seem to be no plans afoot to resolve the situation once and for all.

Despite its location, after World War I, Kuzminki was set up by the Soviets to test their newest chemical and biological weapons.

When the authorities decided to move it further out in the 1940s, the clean-up operation was rudimentary at best.

“I was fifteen and a volunteer. We were told to bury the toxic waste in the ground. There were test tubes, barrels, special suits. We dug out a 1.5 meter-deep trench, and just flung them in,” says Boleslav Grokholsky, a former waste-removal volunteer.

Some of the waste was dug up again and removed, but most was never found.

A quarter of a century later the park was opened to the public.

The removal of toxic chemicals would be expensive – an operation on a similar site in the US in 2005 cost over half a billion dollars.

“We need a study to evaluate the exact level of risk in order to understand what the exact risk of contamination is, and what we should do next,” says Efim Brodsky from the Institute of Ecology and Evolution.

So far, no such official study has been published.

In the meantime, Moscow’s park-goers will just have to hope that the only burns they get are from the summer sun, while below them lies an artifact from history they’d rather not learn about.