Regret vacation

To get to the vacation on the Level Regret, play the level up until the point where you have exited the second underwater elevator. Continue to the area outside swarming with enemies, kill all the enemies and wait for the pelican arrives. When the pilot says "This is my last run Chief", look for a small bulge of land near the far left of the hill wear the Elites were. Jump on this ledge and when the Pelican has lowered near to the ground, jump onto the Pelican and hang on and jump of at the ledge in the direction wear the Pelican will be flying towards (you may need to time the jump a few times or else you will die) and continue to the mountain on either your left or your right side. The smaller mountain on the right is easier to climb, but you must stay on the pointy ridge of the mountain as you reach the top or else you will fall to your death. The same can be done with the other mountain but you can also climb up the other path facing the mountain foothills, but this will take more time. On the larger moutain you will be so high that some parts of the level will "fade away" as you get higher. At any point you can return to the level, simply backtract carefully and jump of the small ledge.