  In recent years, more and more exotic hadronic states have been discovered
successively. Many of them can be explained as hadronic molecules, such as
$D_{s0}^*(2317)$, $X(3872)$, and $P_c$ pentaquark states. Analogous to the
formation of nuclei, we study three-body hadronic molecules with the Gaussian
expansion method and predict the existence of the $DDK$,
$\Xi_{cc}\Xi_{cc}\bar{K}$, and $BB\bar{K}$ bound states, which are likely to be
found in the current and updated facilities.
