Yes, there are places you can mail a letter underwater. Gadling lists five of them. Link -via Dump Trumpet
I'm a bit bummed that you can't order a postcard from there and mail it to yourself. Oh well, looks like I'll have to go there and do it myself. ;-)
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Moe, that's a great idea! This would be an easy way to generate a little extra revenue for the local communities.
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