  We present a study of the Corona Borealis (CB) supercluster. We determined
the high-density cores of the CB and the richest galaxy clusters in them, and
studied their dynamical state and galaxy content. We determined filaments in
the supercluster to analyse the connectivity of clusters. We compared the mass
distribution in the CB with predictions from the spherical collapse model and
analysed the acceleration field in the CB. We found that at a radius
$R_{\mathrm{30}}$ around clusters in the CB (A2065, A2061, A2089, and Gr2064)
(corresponding to the density contrast $\Delta\rho \approx 30$), the galaxy
distribution shows a minimum. The $R_{30}$ values for individual clusters lie
in the range of $3 - 6$ $h^{-1}$ Mpc. The radii of the clusters (splashback
radii) lie in the range of $R_{\mathrm{cl}} \approx 2 - 3$ $R_{\mathrm{vir}}$.
The projected phase space diagrams and the comparison with the spherical
collapse model suggest that $R_{\mathrm{30}}$ regions have passed turnaround
and are collapsing. Galaxy content in clusters varies strongly. The cluster
A2061 has the highest fraction of galaxies with old stellar populations, and
A2065 has the highest fraction of galaxies with young stellar populations. The
number of long filaments near clusters vary from one at A2089 to five at A2061.
During the future evolution, the clusters in the main part of the CB may merge
and form one of the largest bound systems in the nearby Universe. Another part
of the CB, with the cluster Gr2064, will form a separate system. The structures
with a current density contrast $\Delta\rho \approx 30$ have passed turnaround
and started to collapse at redshifts $z \approx 0.3 - 0.4$. The comparison of
the number and properties of the most massive collapsing supercluster cores
from observations and simulations may serve as a test for cosmological models.
