From Saturday until Thursday, a duplicate of the Large Hadron Collider (LHC) will be on display in the Senedd building in Cardiff Bay.
Visitors will be able to walk through the tunnel, with physicists on hand to explain the machine.
The LHC is 16.7m (27km) in circumference and straddles the border beneath Switzerland and France.
A life-sized model of a section of the most powerful particle accelerator in the world has gone on show in Cardiff.