The correct way to complete the sentence is:

"I would travel around the world if I were very rich."

This sentence uses the second conditional, which is used to talk about hypothetical or unreal situations in the present or future. The structure is:

- "would" + base form of the verb (for the result clause)
- "if" + past simple (for the condition clause)

So, "I would travel" (result) and "if I were" (condition).