Real walking is the most natural method of navigation in virtual environments. However, physical space limitations often prevent or complicate its continuous use. Thus, many real walking interfaces, among them redirected walking techniques, depend on a reorientation technique that redirects the user away from physical boundaries when they are reached. However, existing reorientation techniques typically actively interrupt the user, or depend on the application of rotation gain that can lead to simulator sickness. In our approach, the user is reoriented using portals. While one portal is placed automatically to guide the user to a safe position, she controls the target selection and physically walks through the portal herself to perform the reorientation. In a formal user study we show that the method does not cause additional simulator sickness, and participants walk more than with point-and-fly navigation or teleportation, at the expense of longer completion times.