If I recall for TRS2004, there is also:
alt+FLY to "fly" above the ground and move around. Use the arrows.
alt+WALK puts you at the ground level so you can walk on the terrain.
This is different than placing the camera on the ground because you can move over hills instead of bumping into them. I used this all the time to get a Trainzperson's view of their world. It's really great for checking for floating objects such as splines and buildings next to hills.
John