A method for operating a navigation device including a processor, a signal receiver for receiving position signals, a road network database that also contains position data on tunnels (tunnel attributes), a position finding unit that determines the current position of the vehicle, a display unit and a display control for controlling the adjustments of the display unit, particularly for regulating the brightness and/or a color scheme of the display unit. The display control is able to change the adjustment of the display unit while driving through a tunnel (tunnel mode). The method can include determining the vehicle position with consideration of the received position signals and automatically activating the tunnel mode of the display unit by means of the display control immediately or with a certain time delay if the determined vehicle position features a tunnel attribute and the received position signals fall short of a predetermined signal quality.