What happens when you start running on an innocuous looking gooey liquid and then stop? And what about when you look at the world through reversing goggles? Judging by the looks on children's faces, what matters most is the fun of it, but it is also a precious hands-on learning experience.

After days of heavy downpours, the sun shone again in Ljubljana on 1 June, just in time for the 15th Znanstival, a three-day festival of all things scientific organised by the House of Experiments where kids and adults alike can do hands-on science.

Laughter, delight and applause filled the streets and bridges of the old town. There were science experiment stations set up at every turn, and clusters of children gathered in front of them, curiously observing what was happening.

It was particularly lively at the iconic Triple Bridge, where a real spectacle was taking place. Children were queueing to try walking on a seemingly gooey cream-coloured substance known as oobleck.

They had to get from one end to the other without their feet sinking into the morass. One young visitor, Gal, passed the test with flying colours. "I had to run really fast. If you don't run fast, your legs sink and it's harder to get them back up," he said enthusiastically while encouraging his friends to take part in the challenge.

"The liquid is actually a mixture of water and cornstarch. In just the right proportions, such a liquid behaves like a solid when you apply enough force to it, for example when you run on it, and like a liquid when that force stops or you stop," explained Alenka Mavri from the House of Experiments.

On nearby Mačkova Street, stands with various experiments were packed close together, among them a special four-legged robotic dog that drew huge crowds of the tech-curious. And in Town Hall, visitors entered the world of particle physics.

"We have an exhibition here to celebrate the 70th anniversary of CERN, the European Organisation for Nuclear Research and the world's largest particle laboratory," said Tadej Novak, a researcher at the Jožef Stefan Institute, who is at CERN researching particle collision simulations in the Smash project at the CERN Accelerator.

The exhibition showcases the work of the researchers at CERN, and visitors can also play "proton football," a game in which they learn about the Higgs boson and see how proton therapy is improving everyday life.

Near the Dragon Bridge, Miha Kos, director of the House of Experiments, invited us to board a very special bus.

Together with the visitors, we went on a half-hour ride full of interactive experiments, where we observed, for example, what happens to a balloon filled with helium when the bus is moving steadily, accelerating or decelerating.

All in all, there were around a hundred shows, lectures and workshops over three days, hosted not just by the House of Experiments but also by foreign guests.

"Znanstival is an event where we promote not science, but the scientific way of thinking. What we do, and what schools and parents should do, is to create a safe environment for making mistakes. Curiosity should be encouraged and mistakes should be rewarded," stressed Kos.