A few weeks ago I decided to learn OpenGL.  I've wanted to learn it for a long time and I found myself with a few free days over Christmas.  Once I got started, I just couldn't stop.  It's a very interesting technology and it's not too hard to learn.  If you're interested in getting into this, I highly recommend the tutorials from Nehe.

Landscape
This program reads in a Terragen terrain file, maps a texture onto it, and allows the user to move around in real time.  Download a zip file with a sample terrain and texture map.  Type landscape at a command prompt for usage information.  Page Up/Down moves the view up and down.  Up/Down arrows translate the terrain.  Left click and move the mouse up and down to rotate around the y-axis.

TrianGL
One of the hardest parts about creating nice looking OpenGL graphics is manually writing out all the triangles to make up a picture.  To save some time, you can use a 3D modeler (like AC3D) and save the output as a list of triangles.  TrianGL reads in a list of triangles from AC3D and creates the model in OpenGL.  Download a zip file with the program and a sample triangle file.  Type "triangl tie.tri" at a command prompt to run the program.  You can move the object around by left clicking and dragging your mouse (or use the arrow keys).  Page Up/Down zooms in and out.  Toggle full screen with F1.  Reset the view with F2.  Toggle free spin mode with F3.