On 14-15 September 2019, CERN opened its doors to the public for its first Open Days since 2013. This massive event saw over 75,000 visitors descend upon the Organization – many of whom eagerly anticipated underground visits to the LHC and its experiments.

These large crowds were met by almost 300 ATLAS volunteers, whose adaptability and enthusiasm helped ensure the best possible experience for the greatest number of visitors. Volunteers guided around 3800 visitors underground to see the ATLAS experiment and nearly 1500 to the ATLAS control room. This was significantly more than anticipated and set a new record for ATLAS visits.

"The Open Days at ATLAS and Building 191 would not have been possible without our volunteers’ enthusiasm, dedication, and great, unstoppable willingness to explain ATLAS science to the public,” said Karl Jakobs, ATLAS Spokesperson.

Feedback from visitors was exceptional, with several underground guides receiving personal thanks via social media and email. “Visiting CERN is something I've wanted to experience for at least for 20 years,” wrote one visitor. “To get to see things like the ATLAS muon spectrometer and calorimeter down in the cavern was so exciting (to that extent that my hands were a bit shaky).”

“I was particularly impressed by the three high-school students in our ATLAS visit group, who had saved money all summer and travelled from Belgrade to attend the Open Days,” said another visitor. “Their future is bright, and I am sure they will work at CERN one day.”

Exclusive to the CERN Open Days, the collaboration also opened Building 191 (the "ATLAS Detector Workshop") to public visits. This was a unique opportunity for visitors to get up close to ATLAS' New Small Wheels and enjoy hands-on experiences with real detector pieces.

The Open Days tested the resourcefulness of ATLAS volunteers and visitors, as queues at Point 1 quickly began to fill. To encourage visitors to explore other visit points, ATLAS volunteers spontaneously began organising walking tours through the CERN Meyrin campus to Building 191.

Despite the two-kilometre walk (one way!) in hot weather, these tours proved a resounding success. ATLAS volunteers successfully led 15 walking tours over the course of the weekend, with some tour groups reaching up to 100 people. Not only did these tours ensure that visitors correctly navigated the Meyrin campus to reach the remote workshop, they also gave visitors a chance to explore CERN with a "local".

Open Days visitors also took part in several hands-on activities at the various ATLAS stalls, learning about particle physics and the research carried out by the ATLAS Collaboration. At the Point 1 stalls, the numbers speak for themselves: ATLAS "baristas" discussed physics with an estimated 2000 visitors; over 1800 proton cookies were made and enjoyed; kids of all ages designed nearly 300 LEGO particle detectors; and 1150 "selfies" with the ATLAS detector were printed.

So whether you waited in line for an underground tour or just popped by for a proton cookie, thanks for sharing your time and enthusiasm with us during the CERN Open Days.

If you didn't have a chance to join us, remember that CERN and ATLAS can be visited all year round! Head to visits.cern for more information.