system
Given the following post, respond as if you're commenting on Reddit:
human
Archeologist, and those who study Native Americans: Do we know of any large areas of North America that were never explored by native Americans?
gpt
While there are certainly areas where no archaeological remains have been found, it's nearly impossible to know if no native ever explored an area.  If all they left behind is footprints and all they took with them were stories that have been lost in time...

One might think the best bet for unexplored terrain would be the extreme far north, such as Ellesmere island.  However, there is evidence that this area was inhabited both by the Dorset (who were probably related to other native american populations but are now extinct) and the Thule (present day inhabitants who came from Asia in the middle ages).  There were also likely some viking explorers in the area during the period when Greenland was settled and vikings traded with the Dorset and Thule.  

There are areas in Northern B.C. that remain remote and difficult to travel to today, even with modern technology.  For example, it is estimated that more people have walked on the moon than have been through some parts of the stikine river valley, which has some of the most difficult rapids in the world inside of a deep canyon.  It is unlikely that natives could have successfully explored such areas as they wouldn't have had durable modern kayaks or, likely, the deathwish necessary to paddle into that canyon.  However, it's not impossible.  

Perhaps the only sure bet for unexplored terrain is any area recently uncovered by retreating glaciers.  If a place was under a kilometer or two of ice until the last few decades, it was not accessible to native americans during prehistory.

As remote as some places are today, it is important to remember that 99% of Archaeology is done no more than a couple hours drive from the nearest pub.  It's not that archaeologists are lazy, it's just that it's incredibly difficult and expensive to survey remote areas and more difficult still to dig there.  There have been significant finds in the last few years thanks to the availability of satellite imagery of remote areas.  However, such imagery, no matter how well massaged by algorithms, can only reveal relatively large features, such as buildings.  With only a few exceptions (e.g. the mound builders of Cahokia), large structures were not built by natives in North America.  There are, no doubt, many archaeological sites we have yet to discover, especially in remote areas where humans seldom tread even today.