DNT routes developed in part from older thoroughfares and local footpaths and in part in response to the needs of trekkers, as ensured by the public right of access. They serve both to guide trekkers, on foot or on skis, and to protect plant and animal life by serving as limited channels for most human foot traffic in the outdoors.
All DNT routes are clearly waymarked at intervals sufficiently short so you can see from one waymark to the next, even in fog and rain. They are of two types: summer hiking trails and winter cross-country skiing tracks.
in the mountains are waymarked with red letter Ts, painted on cairns and rock walls. In forested areas (e. g. around Oslo) and along the coast, waymarking is with blue strips painted on trees or poles. Summer waymarking is permanent and can be seen year-round. In all, there are some 20,000 km of T-marked routes.