If at first you don't succeed..
Number of lemmings that drop: 100
99% to be saved
Release rate: 40
Available time: 04:00
The first lemming should bash through the first two pillars and mine through the third one. Now mine through the obstacle. When there is a passage, build to stop mining. Now build stairs to the exit. Remove the blocker in time otherwise you will run out of time.
Some alternatives were sent to me by Nortaneous on 27 December 2010:
You don't need a blocker; just make the first lemming an athlete and send him over the first pillar, and then bash through it later, once the stairs are mostly built. Also, here's how I do it: Instead of mining through the third pillar, send two athletes over. Make the first one climb over the other two pillars and build stairs, going as far to the right of the floor as possible, and make the other one mine/dig downwards and bash to the right through the floor. Actually, it'd probably be possible to modify that slightly and solve the level with no excavation tools except a basher and a digger (or hell, even a basher and a bomber or two), but unfortunately, DMA gave that level enough abilities that that's not necessary.
Last edit: Wednesday, 14 May 2008.
Main source: own words.
Graphics: Lemmings, Amiga platform.