Example output from the cooling/heating test problem in diffhydro. Shown are midplane slices through an 384³ ISM-like box evolved from turbulent initial conditions with Ornstein–Uhlenbeck (OU) forcing and the cooling/heating module enabled. Top: logarithmic gas temperature, spanning the cold to warm neutral phases, with cooling producing sharp temperature contrasts in compressed regions. Bottom: logarithmic mass density in the same slice, exhibiting a connected network of overdense filaments and shells generated by the driven turbulence. The close spatial correspondence between cold structures and density enhancements, and the warm/hot volume-filling background, illustrates the emergence of a multiphase medium and demonstrates that the implemented cooling/heating routines couple self-consistently to the turbulent flow.