An inland place near Cairns - the so called "Atherton Tablelands" - makes an interesting afternoon drive. Very mellow and flat, though despite this it is oddly enough easy to get lost driving around in. Take a GPS or Map. I was bored with Cairns and went out there. Very glad I did. Could be something to do post-dive if you're killing time waiting for your flight.

P.S. Do not, no matter how bored, take the boat up north to Cooktown. You will spend hours getting up there, five minutes looking around, then wait two hours to leave. Enough said.