To the Lofty Summit requires you to Complete all Area 3 levels on Insane.
Area 3 levels are listed as the third set of levels after the second boss and including the third boss. The difficulty setting must be on Insane to get credit for this achievement.
The Crown of the Beast - Completed all Area 3 levels on Hard
To the Lofty Summit - Completed all Area 3 levels on Insane
Team Effort - Completed all levels with 4 active players on >= Medium Difficulty
A Matter of Perspective - Saw all four Hero endings
Dungeon Defender - Completed all levels on Insane! Congratulations Brave Dungeon Defender!