Antarctica 88 (UP)

I recommend playing on the Ghost difficulty and the enemies won't be able to see or attack you and you can run right past them.

To get the medium ending you must do only one of the optional objectives.

You can do either objective below.

#1 Blow up the lab with samples: This is the area where you found the Snowmobile, you need to place dynamite on the big propane tank where you picked up the gas tank for the Snowmobile.

#2 Blast the entrance to the caves: This is the drilling area where you can go down the ladder to the caves.
You'll find another propane tank next to the left of the ladder in the drilling area and you need to place dynamite on it.

You can also make a save at the Radio Tower before doing the optional objectives to make mopping up the other endings easier. You can reload your save at the Radio Tower instead of playing through the entire game again.

Here's my Achievement Walkthrough with commentary.

NOTE : Don’t collect all the pages

(Make a save at the radio station)

For this you just have to backtrack after the radio station and just blow the lab up and back track and Escape on the heli .