Relativistic heavy ion collisions create a hot and dense nuclear matter. It has been discovered the matter is in fact a multi-parton system, where the quarks and gluons are free from confinement into hadrons. After the long search for the ultimate state called Quark Gluon Plasma has successfully concluded, a new stage has begun to look into physics under extreme conditions, not only the high temperature (several trillion kelvins) but also the restored chiral symmetry (at least partially), the perfect fluidity (near the quantum limit), and the most intense magnetic field in the universe (a few orders above the magnetars). The history of this interesting field of research will be briefly summarized, and ongoing and near-future challenges to physics under these extreme conditions will be discussed.
