I think it is located behind the front bumper on the left side:
Volkswagen Workshop Manuals > New Beetle L5-2.5L (BPS) (2006) > Instrument Panel, Gauges and Warning Indicators > Outside Temperature Display > Outside Temperature Display Sensor > Component Information > Locations
Volkswagen Workshop Manuals > New Beetle L5-2.5L (BPS) (2006) > Instrument Panel, Gauges and Warning Indicators > Outside Temperature Display > Outside Temperature Display Sensor > Component Information > Locations