According to Graham Timms, the only school outing that could beat it would be flying to the Moon.

The head of science and 11 of his A-level students from The Maelor School in Wrexham walked where no other student party has ventured before during a trip to Switzerland last November.

Mr Timms and his physics pupils were allowed to explore the 17-mile tunnel at the Cern particle physics laboratory in Geneva - the site of the Big Bang machine and the world’s greatest ever science experiment.

The machine was switched on last week by Swiss-based scientists in an attempt to recreate the conditions of the expanding cosmos after the Big Bang.

But despite doom-mongering predictions in the press that the experiment would create a black hole and destroy the Earth, Mr Timms and his A-level cohort had no premonitions of the apocalypse during their trip.

Mr Timms told TES Cymru: “I could allay any fears of doom - we had inside knowledge.”

The Maelor students were let into the tunnel on the Swiss-French border by a stroke of good luck.

Mr Timms found the project leader, Lyn Evans, was a Welshman originally from Aberdare, and he asked if they could meet. Mr Evans obliged, and went further by letting the students explore the tunnel.

“The students were on such a high because they realised that they had been so privileged to go into this tunnel where no member of the public had ever been,” said Mr Timms. “They understood the enormity.”

“It may be one of these Einsteinian turning points in physics. It was really mind-blowing - a physics teacher’s dream.”

All the students started university this month, and all except two enrolled on physics or science courses.

Mr Timms hopes publicity surrounding the Cern experiment will spark more interest in physics and stop the decline in the number of students studying the subject at GCSE in Wales.

This year there were 34 fewer entries for A-level than in 2007.