Duathlon!
The custom distance is about a 10 K run, followed by a 20 K bike ride, then finish off with a 5 K run.
It is a great challenge and is verry addicting.
However, if you can find a pool to swim at I'd definitely encourage it. From personal experience, a triathlon is unlike any other similar athletic event such as the duathlon or aquathlon. Once you start you'll be addicted!