One of the hardest levels in the Tricky difficulty, rightfully so. You must save every Lemming, and your resources are very limited, unlike in the Fun difficulty, where you could simply use Builders to your hearts content.
Make the first lemming a Climber, and a second one a Basher, when he reaches the wall. Let your Climber near the exit but do NOT let him enter. Instead, dig a little hole - just a little - then apply a Builder skill to make him turn around and go to the left. Now it's mining time! Give him a Miner ability, accordingly to the vertical hole, where the Basher is currently heading. This is obviously the hardest part, since you must be quite accurate where you apply the Miner skill - if you apply too early, he'll dig himself out of the level, and you fail. If you apply too late, the tunnel of his will not be low enough for the Lemmings to enter. It may take several attempts to figure out the right time.
This map is one of the first true puzzle levels of lemmings, and caught a lot of novice players off guard. It got so infamous that the solution was actually printed in the instruction manual of the Genesis/Megadrive version.