The heat transfer between a solid body and a surrounding fluid is a major process in many natural and technical flows. It has been studied experimentally in the so-called "Barrel of Ilmenau" โ a large-scale Rayleigh-Bรฉnard experiment with a height of eight Meters and a diameter of seven Meters. In our work, we focused on the flow field close to the horizontal plates as well as on the interface between these so-called boundary layers and the well-mixed core region. The flow field close to the plates, but also in the bulk region is very complex and three-dimensional and a comprehensive characterization requires volumetric flow measurement technique. In a first work package, we measured it in the vicinity of the cooling plate using tomographic Particle Image Velocimetry technique. The measurements have been undertaken at Rayleigh numbers between ๐ ๐ ๐ ๐ =10 8 und ๐ ๐ ๐ ๐ = 10 12 at fixed aspect ratio Gamma = 1 and fixed Prandtl number ๐๐๐๐=0,7. We found that the boundary layers in turbulent Rayleigh-Bรฉnard convection start to become turbulent already at a Ra number as low as ๐ ๐ ๐ ๐ โ 10 9. At๐ ๐ ๐ ๐ โ10 12,turbulence dominates the near-wallflowfield.Inorderto studythe evolution of plumes and their interaction with the bulk, we also measured the flowfield in horizontal cross sections through the entire Rayleigh-Bรฉnard cell. Despite a multitude of technical challenges and problems, which are essentially linked to the large size of the measurement field (40 m2),two complete sets of data at aspect ratios Gamma Gamma = 1.4 and Gamma Gamma = 3.0 could be acquired.