I was just trying to make an easy but fun level right now... and I accidentally ended up making one of the hardest levels I've ever made. (As in, the terrain layout that I put together allowed for it, and I saw the skillset and stats that would acheive it). The original intended hard solution didn't work(was impossible), but by pure accident I found that by simply adding one more miner an even harder one would work, and after about fifty attempts, I finally managed to pull it off successfully.
http://www.megaupload.com/?d=NL12RZ1PThere's the level itself (in .LVL format), the BMP image of it, and a TXT file with the solution.
The level is designed for and tested in Windows Lemmings, and I actually doubt this one will play correctly or even be possible in the DOS version.