These pieces have been made to be used with D&D miniatures. I've tried to keep things as simple as possible, therefore some of the rules may sound a little weird; And originally this page has been made some 5 years before moving it to current site... but it has a nice collection of terrain piece images so I wanted to add it here.
Pillar. Considered as piece of wall.
Single tree. Can't move through it, otherwise handled as a statue.
Single large mushroom. Handled as 4-piece wall, except you can fly over it.
Forest. Blocks line of sight, otherwise handled as a large statue.
Stalagmites, rocks, tombs, graveyards etc. Handled as statues.
Water. You have line of sight and can fly (and can extend command effect) over it, but you can't pass through it otherwise. The bridge is handled normally. Note that you can step to and from the bridge diagonally, as water doesn't block movement.
Stairs. They replace exit corners. For simplicity, We've decided that a creature stepping on the stairs has fled. As a new addition, I'd say that they are considered to be difficult terrain.
Door. It takes movement points equal to full move of a character to open or close a door.
The Dark Altar. Standing on the borders of this altar gives +5 melee damage. Actual altar in the middle gives cover. Just tried it, and it made things really interesting!
Snow. Snow is considered to be difficult terrain. Rock in one square acts like a statue.
Swamp. Swamp slows you down, and if you stay on it after your move... well, don't do it. And avoid getting stunned by AoO's! Again, a rock taking two squares acts like a statue.
Rock. Like a wall, but you can fly over it.
Tower. Too high to fly over in the heat of the battle.