So the Shortcut achievement requires you to find a way to the Alien City without going into the Treemen's Domain, and Daredevil requires you to get to the Alien City without activating any checkpoints.

If you don't have the Shortcut yet, it'll be easy to do these two achievements at the same time, because it's faster and safer this way.

Attempting a Daredevil playthrough is required in order to get the Gauss Gun upgrade. I recommend this guide for any achievements that you may have a problem with:

http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=430099696