Here's a quickie tutorial I threw in. Walk into the "landing zone" to see your ride land... [Editor's Note: A spaceship decends from the sky - gls 12/15/2000] This is a really easy trick to create. It simply involves a buncha platforms that all move in synch, with an identical range of motion. Note that the range of motion doesn't mean they all have the same start and end heights, though. I won't get too involved with the details, but I'll point out a few important aspects:

1. The ceiling must move with the ship. Otherwise, the ship will look as though it's getting bloated. That is to say, the effect won't work because it'll look as though the ship is a platform lowering from the ceiling. (So would not using a landscape texture on the ceiling...)
2. Similar to the above point, the platforms can't come into contact with the static walls. This is to prevent the walls from appearing to shorten.
   

The arrows which are pointing to thick lines around the lowering platforms are actually indicating where a super-thin polygon is located. It needs to be there to allow the effect to work properly.

This polygon has three requirements:

1. It has to be higher than the side walls;
2. It has to be lower than the lowest height the ceiling will end up at;
3. It needs to be extremely thin so that it can't be seen from underneath the ledge. Otherwise, a strip of landscape texture will be visible, throwing off the effect.

I'll assume you've got enough experience with Forge to be intuitive enough to realize what the basic floor and ceiling heights ought to be to prevent any odd chunks of landscape from coming into view where they really shouldn't.