  The discovery of topologically protected boundary states in topological
insulators opens a new avenue toward exploring novel transport phenomena. The
one-way feature of boundary states against disorders and impurities prospects
great potential in applications of electronic and classical wave devices.
Particularly, for the 3D higher-order topological insulators, it can host hinge
states, which allow the energy to transport along the hinge channels. However,
the hinge states haveonly been observed along a single hinge, and a natural
question arises: whether the hinge states can exist simultaneously on all the
three independent directions of one sample? Here we theoretically predict and
experimentally observe the hinge states on three different directions of a
higher-order topological phononic crystal, and demonstrate their robust one-way
transport from hinge to hinge. Therefore, 3D topological hinge transport is
successfully achieved. The novel sound transport may serve as the basis for
acoustic devices of unconventional functions.
