Tortuous microchannels have attracted increasing interest due to great potential to enhance fluid mixing and heat transfer. While the fluid flow and heat transfer in wavy microchannels have been studied extensively in a numerical fashion, experimental studies are very limited due to the technical difficulties of making accurate measurements in micro-scale flows. This thesis provides insights into thermohydraulics of tortuous microchannels by developing experimental techniques and performing systematic visualisation and heat transfer experiments. The detailed flow patterns (including Dean vortices) and transition behaviours in wavy channels are successfully identified using Micro-Particle Image Velocimetry (micro-PIV) and 3D reconstruction techniques. Conjugate heat transfer simulations are carried out to understand the complex thermal behaviour present in the current experimental design and to validate and compare with experimental results. The impact of tortuous geometry on flow and heat transfer in microchannels is studied systematically. The high quality experimental data provide a new perspective on flow behaviour and heat transfer performance in wavy microchannels. In addition, the stackability of channels on a plate is considered. The zigzag pathways are found to provide the greatest heat transfer intensification based on a plate structure. A significant component of the research in this thesis has been the development of experimental techniques to measure local heat transfer rates in microchannels. A two-dye laser induced fluorescence (LIF) technique using temperature sensitive particles (TSPs) is developed with promising characteristics for local temperature measurement and the capability for simultaneous measurement of temperature and velocity fields in microscale systems. The advanced experimental techniques developed in this thesis provide important tools for the investigation of thermohydraulics of various micro-devices in the field of engineering.