Nordkalottleden is a hiking trail of 800 km total lenght, starting in Norway, passing through Sweden and Finland and ending in Norway again. It touches Treriksröset, where the borders of the three countries have one point in common. Conditions along the trail are varying greatly. On some of the sections cabins are available where provisions are sold, on other parts you have to carry all provisions and stay in a tent.
Peter Bickel wrote the only book (in German) with a complete description of Nordkalottleden that I know. There is information about his book on his homepage www.nordskandinavien.de. He answers questions about the trails and his book, and his email-address is: firstname.lastname@example.org