For decades, antiferromagnets have been viewed as the “interesting but useless” siblings of ferromagnets. While they offer the promise of faster, denser and more robust magnetic memory, they remain “invisible” -- difficult to detect and control because their internal magnetic moments cancel out. In this colloquium, I will highlight my journey in discovering the momentum-dependent non-relativistic spin splitting (NRSS) in symmetry-breaking antiferromagnets. Despite having zero net magnetization, these materials exhibit split energy bands with opposite spin polarization -- a characteristic feature typically reserved for ferromagnets (FMs). This resemblance to FMs endows them with a multitude of exotic physical properties, leading to the recent coining of the term “altermagnet”. This phenomenon, first hinted at by Pekar and Rashba in 1964 as arising from the intrinsic inhomogeneous magnetic fields, represents a paradigm shift in how we perceive antiferromagnetic materials, providing a new way to detect and manipulate these “invisible” magnets.