  The $\Omega\Omega$ system in the $^1S_0$ channel (the most strange dibaryon)
is studied on the basis of the (2+1)-flavor lattice QCD simulations with a
large volume (8.1 fm)$^3$ and nearly physical pion mass $m_{\pi}\simeq 146$ MeV
at a lattice spacing $a\simeq 0.0846$ fm. We show that lattice QCD data
analysis by the HAL QCD method leads to the scattering length $a_0 = 4.6
(6)(^{+1.2}_{-0.5}) {\rm fm}$, the effective range $r_{\rm eff} = 1.27
(3)(^{+0.06}_{-0.03}) {\rm fm}$ and the binding energy $B_{\Omega \Omega} = 1.6
(6) (^{+0.7}_{-0.6}) {\rm MeV}$. These results indicate that the $\Omega\Omega$
system has an overall attraction and is located near the unitary regime. Such a
system can be best searched experimentally by the pair-momentum correlation in
relativistic heavy-ion collisions.
