Aside from these major tramping tracks, which also offer guided walks, dozens of lesser known tracks are maintained by the Department of Conservation, ranging from tracks requiring intermediate skills, such as the Hump Ridge Track and the Lake Marian track to advanced multi-day hikes like the Dusky Track and several routes that should only be attempted by experienced trampers. Fiordland is a challenging tramping destination, and given the size of the national park, there are few tracks. Off-track travel by expert trampers often relies on following deer trails. Sandflies, flooding and poor weather are a hazard, and being stranded for a day or two due to flooded river crossings is not uncommon on tracks like the Dusky Track. Trampers on these remote tracks also face three-wire bridges, tree falls, and rough terrain where mud can be knee-deep.