Using Unity to Create a 3D World
Unity 3D is a program that you can download for free. It works on Macs or PCs. The website is Unity 3D.com
I have made two quick intro videos to get you started:
Part One: Getting Started with Terrains
Part Two: Terrains and the First Person Controller
Part Three: Making Valleys and Holes in Your Terrain
Making Triggers in Levels Using C# Code
Part One: Setting Up Your Triggers
Part Two: Working with Code
Part Three: Putting it Together
Using Audio in Unity
Part One: Using Audio In Unity
Project: Create a terrain with mountains, and a first person controller. Include some sort of valley or hole in your Terrain.
Then, link three levels together with triggers. Add at least three audio files to each level.