Here is the full list of all 14 Hidden Deep achievements.
Ride a elevator from top to bottom non-stop. Yes, that's possible.
Find a hidden cave using the Terra-Scanner
Kill 1000 monsters
Complete a level with high enemy presence without dying (must be 50+ enemies)
Fall from 50 meters or more
Kill 5 enemies in a row while hanging on the grappling hook
Kill the ceiling tentacle before it kills you on your first encounter
Drill 100 meters of tunnel using the Tunnel Boring Machines
Let another team member use your rope to climb
Kill 100 monsters
Rappel down the full length of your grappling hook's line
Use the grappling hook as a zip-line
Kill 3 enemies using one Scan-Ball
Kill 20 enemies with your gun without dying