We present three-dimensional (3D) micromixers realized in a monolithic glass substrate using a simple oblique powder-blasting microfabrication method and a single photosensitive elastomeric mask. The mixer topology consists of a curved microchannel that incorporates a series of nozzle-diffuser elements buried inside the glass substrate. The strongly varying microfluidic cross-section of these elements and multiple channel bends result in the generation of multiple vortices. This results in achieving a high mixing index by chaotic advection, as visualized by a phenolphthalein-sodium hydroxide colour reaction, for flow rates in the range of 2 to 200 μl min-1.