In this paper, horizontal solidification of gallium in a rectangular cavity was studied both experimentally and numerically. Two three-dimensional (3D) numerical models related to different numerical approaches were built. The first is a single-domain (SD) model based on the volume-of-fluid (VOF) method. This model also takes into account the presence of a mushy zone. The second model is a multidomain (MD) one; it includes two different meshes for the two phases and uses Stephan's boundary condition to determine the front velocity. The 3D models were tested under various thermal boundary conditions and compared with experimental results obtained in an appropriate experimental setup. The experimental setup included an ultrasonic Doppler velocimeter (UDV) for noninvasive measurements of the velocities in the liquid part of the metal, liquid–solid interface position and profile, its displacement, and longitudinal mean velocity. For determining the boundary influence, both 3D and 2D models were built. The comparison was carried out for the solidification front location and shape and the velocity and temperature fields. In general, the 3D numerical model gave more accurate results than the 2D model with respect to the experiments results. Although the MD model is more complicated to build and requires more computational efforts than the VOF model, the 3D MD model provides the most accurate results in comparison with current experiments.