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The concept behind this article is an extensive analysis of the most recent findings about free convection thermal flow in an enclosure or cavity, as well as the methods employed to enhance heat transfer (HT). There are different heat transfer enhancers such as (a) nanofluids, (b) porous media, (c) large particle suspensions, (d) phase-change devices, (e) flexible seals, (g) fins and microfins, and (h) ultra high thermal conductivity composite materials. The majority of heat transfer enhancement techniques that use porous media, fins, and nanofluids are reviewed in the literature. In this review, both experiments and theoretical studies on different cavities are highlighted through investigating the subsequent parameters: impacts of the configuration of the cavities, effect of the type of nanoparticles, significance of cavities in nanofluids, effects of the cavities' tilt angle, wave amplitude, the magnetic field's (MF) influence in cavities, and cooler and heater impacts. Through a review of the literature, it was found that the use of nanofluid in all forms of cavities increases its thermal performance. The most used cavity is square, which has many applications. The results obtained from previous studies can be used to improve the design and heat refinement of the geometry applied in diverse energy systems. Additionally, as the Hartmann number rises, there is a rising tendency observed in the average Nusselt number. Furthermore, as the concentration of nanofluid particles and Rayleigh numbers rise, so does the rate of heat transfer. The heat transfer within the cavity is improved by the hybrid nanoparticles. The amount of the augmentation would, however, decrease as the concentration of nanoparticles increased. The lowest volume fraction of nanoparticles, Ø = 0.2 vol.%, showed the greatest increase. Also, the inner wave affects the flow pattern when the wave amplitude rises but the flow strength stays constant. The most important findings showed that the heterogeneous porous medium transfers heat more effectively than the homogeneous porous medium in different enclosures. [ABSTRACT FROM AUTHOR]