When a viewer peers through the tube, he sees the landmark through the other end.
Ingenious, isnt it?
This is what a viewing tube looks like.
Photo credit:leloupdujura/Imgur
This particular viewing tube is located somewhere in the Swiss mountains.
Viewing tubes in the Swiss mountains.
Photo credit:leloupdujura/Imgur
A viewing tube near Mt Whitney.
Photo credit:Research-Indicates/Reddit
Mt Whitney through the viewing tube.
Photo credit:Research-Indicates/Reddit
A viewing tube near Brigham Butte.
