A major European power boasts the world's longest road tunnel, which stretches more than 15 miles and features striking design and lighting.

Laerdal Tunnel, which cost some £120m to build, links the Norwegian municipalities Laerdal and Aurland, also became the final link on the main highway connecting the capital Oslo and Bergen.

Connections between the two areas had been limited with only ferry connections and difficult mountain crossings which made travel difficult during the winter months, according to Engineering.com.

But while most road tunnels aren't known for being much to look at, Lærdalstunnelen was devised with driver experience in mind, with large, colourfully lit caverns strategically placed every six kilometres (3.7 miles) to keep motorists focused.

Experienced psychologists at SINTEF (the Industrial and Technological Research Association) worked closely with The Norwegian Public Roads Administration on the ingenious breaks in the journey, which serve to split the route up and give a sense of progression, making the 20-minute drive a truly unique experience, according to Road Traffic Technology.

Simulators to test out the light, gentle curves and short straight sections, ensuring the drive was not monotonous while also in line with guidelines for safe viewing distance, as per the outlet.

Work on the tunnel began in 1995 and it was officially opened by Norwegian King Harald V only five years later.

The tunnel also has a large number of safety features including brightly lit emergency telephones and fire extinguishers which appear at more frequent intervals than in other major tunnels.

Monitoring equipment is also used by the NPRA to check that the tunnel's various features, including radio connections, traffic lights and ventilation are functioning correctly.

The tunnel is reinforced and protected by 200,000 rock bolts for the safety of passengers.

One TripAdvisor reviewer said the drive can be a "little disorienting" but is an "amazing engineering feat". "Drive through it and you forget that you are under a mountain!" they added.

Another described the unique passageway as a "true engineering marvel". "Driving through almost 150+ tunnels on my trip across Norway; I was close to getting claustrophobic," they added.

"But this being the longest kept me hooked on with the amazing light display at every 6km interval. There is a place to park near the caves and enjoy the light spectacle. The air quality is amazingly fresh."

The surprisingly clear air is thanks to a cleaning plant for the tunnel ventilation air, which keeps air quality acceptable throughout the tunnel even during busy periods, Road Traffic Technology says.

The area where the tunnel is built is a UNESCO World Heritage site known for its stunning fjords, including the famous Aurlandsfjord nearby.