In the present work, the formation of unmixed regions and material transport in a stirred vessel flow with an anchor impeller, which is common in mixing highly viscous fluids particularly with yield stress, have been investigated by experimental and numerical approaches. Newtonian fluid is employed as a working fluid and flow visualization experiments are carried out with the laser-induced fluorescence technique. Experimental unmixed regions are compared and analyzed using flow simulations with the Poincare section. We discuss formation of peculiar dynamical systems structures in flows of a Newtonian fluid in an anchor agitator: a subharmonic Viking-helmet-like structure with two horns, a central bowl-shape island and an outer toroidal band. The effects of the Reynolds number on the dynamical structures have found to be minor, though there appears unsymmetrical formation of the horns that enhances mixing performance to some extent.