  The exploration of the QCD phase diagram has been one of the main drivers of
contemporary nuclear physics. The Relativistic Heavy Ion Collider (RHIC) at BNL
is uniquely suited for this task through its Beam Energy Scan (BES) program
which allowed for a large range in baryon chemical potential $\mu_B$ as was
successfully demonstrated after the completion of Phase 1 in 2014. Phase 2 of
the BES at RHIC is scheduled to start in 2019 and will explore with precision
measurements the intermediate-to-high $\mu_B$ region of the QCD phase diagram,
five energies $\sqrt{s_{NN}}$ from 7.7 to 19.6 GeV in collider mode and eight
energies $\sqrt{s{_{NN}}}$ from 3.0 to 7.7 GeV in fixed-target mode. Some of
the key measurements are: the net-protons kurtosis that could pinpoint the
position of a critical point, the directed flow that might prove a softening of
the EOS, and the chiral restoration in the dielectron channel. These
measurements will be possible with an order of magnitude better statistics
provided by the electron cooling upgrade of RHIC and with the detector upgrades
planned to improve STAR's acceptance. These proceedings review the BES Phase-2
program and the physics opportunities enabled by these upgrades.
