Nanofluids as new thermo-fluids have found their place in recent heat transfer research. Nanofluids' thermal conductivity is often superior to conventional heat transfer fluids. On the contrary, the viscous nature of nanofluids is more than that of the standard fluids. The most crucial matter in forced convection is finding the optimum nanoparticle concentration to achieve efficient thermal transport, while the increased viscous attribute affects the system's pumping power. However, natural convection has no pumping system, so any heat transfer advantage is passive as it relies upon the thermal conductivity modification of the fluid or the cavity modifications that can contribute to the buoyancy effects. Therefore, natural convection is one area that clearly shows nanofluids' benefit. This research discusses nanofluids' cavity flow natural convection and the effect of essential parameters such as nanoparticle volume fraction/concentration, base fluid, aspect ratio, size of nanoparticles, and hybrid nanofluids. The cavity has two parallel walls, which are differentially heated, while the other walls are insulated. Therefore, different nanofluids have been examined experimentally in a cavity flow. The nanoparticles in this investigation include mono-particle-based nanofluids with Al₂O₃, TiO₂, SiO₂, ZnO, MWCNT, and hybrid nanofluids containing MgO-ZnO, Graphene-Al₂O₃, Fe₂O₃-MWCNT, Fe₂O₃-Al₂O₃, and Al₂O₃-MWCNT. The optimum nanoparticle volume concentration for all cases made the maximum heat transfer enhancement between 0.05% and 0.15%. However, predicting the best nanoparticle and optimal cavity contributing to the highest heat transfer enhancement is difficult without performing many experiments on different design aspects. It highlights the open opportunities for experiments on natural convection to fill the scarcity of documentation.