Read for a clear explanation of how the difficulty levels are chosen.

Easy (green)

Easy trails do not require specific hiking skills. They are suitable for all. Easy trails usually have good paths that are neither long (< 3 km) nor steep/high (< 300 m). The trails are safe, easy to walk on and suitable for children. 

Medium (blue)

Medium trails require basic knowledge about walking on uneven terrain, a reasonably good level of fitness, and decent hiking equipment (such as good hiking shoes/boots).
Blue trails may include stretches that are steep and challenging to walk on. The trails are medium in length (< 6 km) and height (< 400 m). 

Challenging (red)

Challenging trails are for experienced hikers with high energy levels and good fitness. These trails require proper hiking equipment. 
The terrain can be challenging: steep terrain, stretches with stony ground, rivers to cross, and other challenging stretches that may require climbing, for example. 
Challenging trails have no limits regarding height or length of trip.

Expert (black)

Expert trails are only suitable for very experienced hikers with good physical and mental ability to pass through potentially dangerous terrain. One must bring the necessary hiking equipment and be able to use a map, compass, and technical amenities. 
The terrain can be more challenging than on red trails and may include long stretches with steep terrain. The distances are usually long. 
Because black trails can be dangerous, we recommend that only experienced hikers walk these trails. 
Expert trails have no limits regarding height or length of trip.