I have recently been thinking about how to get around the world without polluting it. I concluded that the only way to see the world without putting my footprint on it carbonly speaking is to sail. I have never done it, but with global warming on the increase, I'm thinking it may be my new sport of choice.
...but sailboats still pollute. You have to use a motor to get out of the harbor. These are usually gas-powered. Now, I suppose you could try to rig up your boat to use biodiesel or something, but once you are out sailing around the world, you are then dumping your human waste directly into the ocean. That's not to say that sailing is horribly wrong or isn't better than other methods of transport, but it's far from perfect.