This paper addresses the problem of guidance of unmanned underwater vehicles (UUVs). In the framework of a two layered hierarchical architecture decoupling the system dynamics and kinematics, two guidance laws for approaching a target with the desired orientation and following an environmental feature have been designed with Lyapunov-based techniques. Suitable acoustic-based estimators of the corresponding operational variables have been designed and integrated with the guidance and control system. Experimental results of pool trials of a prototype UUV executing free-space maneuvering and wall-following tasks are reported and discussed.