The Forestry Lookout is one of the locations within Mystery Lake. It can be seen from the Derailment by looking at one of the sides of the rail, and it can be reached from that point, going up the hill towards it (The map on this wiki is misleading, the track from Clearcut doesn't lead there, it leads to a destroyed lookout and a shortwave tower).
This shelter is very useful. It has a wood stove in it, and many supplies you can loot, for example:
Sometimes you can also find: