In the present study, we investigate the characteristics of thermal cavities in the rarefied flow regime using the Direct Simulation Monte Carlo (DSMC). We use a recently developed iterative technique to impose a desired wall heat flux boundary condition in the DSMC algorithm. Fluid mechanics and heat transfer behavior are studied over the walls and in the domain of the thermal cavity over a wide range of Knudsen number in the slip and transition regimes. The vortice behavior is described at different Knudsen numbers in detail. We numerically justify unconventional flow movement from the cold region to the hot region. Finally, we consider the effects of molecular structural parameters such as molecular mass and degree of freedom on the thermal behavior of the thermal cavity flows.