Unlike most places in the US, most Swedish trails do not really have an official trailhead with facilities, maps etc. There are exceptions to this rule of course, but Lunsen is not. There many locations were you can park your car and connect to this trail along Road #255 on the east side, and one popular starting point on the west side of 255 is near the folding bridge Flottsund.
Lunsen is known for roots, rocks, and walk bridges. Even though though the terrain does not give you a lot of elevation, it is not flat. Many rock formations and steps require fairly good technique or a short walk off the bike.
Lunsentorpet is a small public cottage were you could even spend a night even though there are no facilities other than a manual pump with fresh water and fire places. A nice stop to enjoy your snack or coffee from your tour pack though.