This paper presents an experimental and numerical investigation on the natural convection flow and heat transfer in an enclosure with a single-hole baffle at the median height. The temperature in the fluid is quantified by means of temperature sensitive thermo-chromic liquid crystal (TLC) particles. The fluid flow velocity is measured non-intrusively with a full field particle tracking technique. The three-dimensional numerical model, developed and validated with experimental data, provides a computational tool for further investigation of mass and energy transport through the baffle openings in these types of enclosures. The experimentally visualized and numerically simulated flow structures show a pair of streams across the baffle-hole. The two chambers communicate through this pair of streams which carry the fluid exchange and heat transfer between the two chambers. At the baffle opening, the two streams are aligned in a diagonal direction across of the enclosure. The streams are accelerated and form jet-like flows that drive the whole circulation in the chambers. The jet-like flows leave the baffle opening, approach the vertical centerline of the cavity, and finally impinge on the top/bottom walls.