Ello, go to the garagegames website and download the free trial
(TGEA Demo)

When starting the demolevel, press F11 to start the World editor. You can play around with the loaded level or go to File -> New Mission to start a new Level with Terrain.

Press F4 to place objects, F3 to edit them and F11 to switch to switch between edit mode and play mode.

EDIT:
Broozar, the Forge Demo is the new demo. It looks like a small watchable demo only, but just press F11 inside and then start a new Mission.

After pressing F11 you can open a mission. With that demo comes two mission, and one of them has a terrain.

see? it runs well on linux. yay for garage games!

actually, if you want a good example of what Torque can pull off, here's an mmo someone made with it (yes it's torque, GarageGames mentions it on their website):

http://www.dreamlords.com/

More difficult to use than normal Torque and does not offer the same cross platform capabilities as TGE. Besides you can Mod TGE to have shaders so I have never understood the reason why you would ever buy TGEA. GS out.

check the features and you'll see:
http://garagegames.com/products/torque/tgea/featurecomp/

There is some good looking wet rainy shader of Torque3d:
http://vimeo.com/2814500

More infos about the developer of this shader are here:
http://www.garagegames.com/community/blog/view/16083/2#comments

If you did not follow the news: The upcoming Torque3d version will have a
significantly higher price. But they told it will be a cheaper upgrade path from
TGEA customers. The feature set of T3D is not officially announced yet but it
is told to read Collada files, gets better documentation, more modular source
code and lots of new shaders (ambient occlusion as an example).

But it also has to face a hard competition now. Unity will enter Windows
market, C4 got a great terrain (with option to sculpt caves, overhangs) and
Shiva is very cheap now.

hmmm the engine is definately worth the price

Sure, if you are a pro-PRO programmer or have a team of one or are just suicidal or like fixing a broken software or like snobby fanbase or absolutely pathetic customer support or engine documentation that fanboys think is 'complete or better' but is absolutely useless or.. umm.. nevermind.

You know what? Everyone should experience GarageGames. Go ahead and buy it.

I fully agree with ortucis. :p