  High-harmonic generation in solids allows probing and controlling electron
dynamics in crystals on few femtosecond timescales, paving the way to lightwave
electronics. In the spatial domain, recent advances in the real-space
interpretation of high-harmonic emission in solids allows imaging the
field-free, static, potential of the valence electrons with picometer
resolution. The combination of such extreme spatial and temporal resolutions to
measure and control strong-field dynamics in solids at the atomic scale is
poised to unlock a new frontier of lightwave electronics. Here, we report a
strong intensity-dependent anisotropy in the high-harmonic generation from
ReS$_2$ that we attribute to angle-dependent interference of currents from the
different atoms in the unit cell. Furthermore, we demonstrate how the laser
parameters control the relative contribution of these atoms to the
high-harmonic emission. Our findings provide an unprecedented atomic
perspective on strong-field dynamics in crystals and suggest that crystals with
a large number of atoms in the unit cell are not necessarily more efficient
harmonic emitters than those with fewer atoms.
