I have an idea.

A contest in which the contestants are given a box that is 50 pixels long and tall.  You can place whatever you want inside that box (I would recommend that you build a box around the edge) as long as it doesn't go out of it at all and as long as you don't use black pieces to get rid of terrain that does overlap.

Sound good?

Sounds good to me.

When I first read the title I thought it meant pieces. So a competition where contestants are allowed one terrain piece (or maybe two). ;) Or maybe only rectangles. You can make some pretty good levels with just one rectangle.

Wow.......

I thought my "Twenty Second Teaser" was pretty minimal (three terrain pieces, screen area 100x60)..... I'd be very interested to see what anyone could do with just half that space!!!

Yeah, sounds interesting, I'd take part. No black pieces also gives it another twist.
Should the box have (apart to the level borders) the other two borders using steel blocks?

I don't really understand what you're asking.  Do you mean that the left and right borders should be steel?  The top border or the bottom border of the box, or either one, depending on where you put your box, will not be the border to the level.  50 pixels vertical is not enough to go across the screen (thank goodness.  If it was the game wouldn't be quite as good).  So your box can't border the top and the bottom at the same time.  Also, you are allowed to have black pieces, but you can't use them to crop pieces that run out of the box boundaries.  The main purpose of the borders of a box would be to give you the ability to remember where your box is.

Just remember these rules and you will have a valid level
-No objects outside of your 50x50 box.
-Submit the upper left and lower right coordinates of your box with your level.
-No terrain outside of your box.
-Lemmings are allowed to go outside of the box, as that can't really be helped anyhow.
-No black pieces used to make terrain fit inside of the box.  This is because you'd have to have terrain outside of the box to fix the terrain.

I actually had thought to use the level boundaries (e.g. top and left) as two borders for the 50 * 50 rectangle and twice steel blocks (for the example bottom and right) to create the other two borders. I thought neither lemmings were allowed to get out of the borders (which I think would make the idea a little more interesing also), therefore that idea.

Another question is about objects: there are also very large objects (e.g. the entrance), you'd have to let the lemmings come out at about the middle of the box. If again only the trigger area (or for the case of the entrance, the point the lemmings come out) would have to be within the boundaries, then you would have more possibilities and also, not most of the box would be filled with object graphics (which would cause that you don't see terrain being located behind object graphics).

Last question: would it be allowed to place steel areas outside of the box (which you don't see)?

...Well, steel areas can be outside of the box if they must, I suppose.  It could be pretty frustrating otherwise, although I'm not sure there will be many cases where you'll need to make steel outside of the box.

This competition is open until I cut it off, just so everyone knows.

...Anyone in???

-Can you make scenery outside of the box if it doesn't interact with the level?
-Who here thinks we should have to steel area the outsides of the boxes?

Yeah, i'm in. I have a level in a box design that could be scaled down to fit the requirements.