This National Historic Trail in Alaska is the only winter trail in the US National Trails System.
The main trail of 1,000 mile, also known as the Seward-to-Nome Trail, crosses several mountain ranges and valleys.
The additional 1,400 miles of side/connecting trails link communities and historic sites, and were established by Alaskan native Indians and Eskimos to connect their villages.

The trail served as a supply route during Alaska’s Gold Rush in 1910, and was used to transport mail carried by dogsleds. 

Congress designated the Iditarod as a National Historic Trail in 1978. In 2004, the Forest Service signed a decision to establish a commemorative trail system on the southern portion of the Iditarod National Historic Trail. This southern trek of the Iditarod National Historic Trail parallels the historic route between Seward and Eagle River by connecting a series of existing trail segments with new trails segments, totaling around 180 miles. 

Conditions are extreme with sub-zero temperatures and gale-force winds which can cause the wind chill to reach −100 °F (−73 °C).