mission : borlis pass

i have a question about borlis pass mission

In the stone summit camp i found a huge gate that i blow up , right after i blow it up i noticed a lever to open and close it , so i went trough the door and saw 999999 enemy's there. but i'm affraid im gonna die trying to destory that baliska.

any suggestion/help?


EDIT : i died after 3 hours of doing that mission