A full-scale exercise took place in the Northern Link tunnel network in Stockholm in September 2022. The exercise scenario was dynamic and consisted initially of a traffic incident involving three passengers cars. It was an escalating scenario and following the incident, one of the three cars was set-up to catch fire. At a later stage, the extent of the exercise increased further when two vehicles downstream of the initial incident were assumed to crash due to limited visibility. Emergency services taking part in the exercise included the fire brigade, police, the local road assistance unit and tunnel operators. The drill provided the emergency services a rare opportunity to practice in a tunnel environment. The exercise also provided opportunity for the tunnel owner to test their tunnel systems, including the fixed fire-fighting system (FFFS). The authors of this paper were responsible for planning, coordinating and leading the exercise. Within this paper, lessons learnt from both the perspective of emergency services taking part in the exercise and tunnel owner acting as observer are shared. The paper also aims to share insights and lessons learnt from a planning and conducting perspective. The drill stressed the need for future exercises. This was highlighted by several emergency service organizations. The exercise clearly shows that the majority of practicing organizations generally have low orientation skills within the tunnel network. In addition, the exercise highlighted that there is a need to practice how active safety systems, e.g. ventilation and FFFS, should be used. That this requires collaboration between rescue service personnel and control operators is clear.