I have to agree with Brain - he always misspells his name out of modesty - about RJ - it's about the easiest way you're gonna be able to dive there staying at the airport. If that's a hassle or he's not running, truck on down to Coral Gables and plunk your jet-lagged carcass in the Venetian Pool for a spell. Coral Gables is still the only city I've been in that has valet parking for the meters.
http://www.venetianpool.com/
Hey listen - don't listen to these Miami naysayers. There's a ton of stuff to do down there within a 6 mile radius of the airport that does NOT involve or require the use of large caliber firearms to have fun and/or remain in the upright vertical position.
Uh, wait a second - lhpdiver - that's Lighthouse Point, right? You know all this stuff then and I'm just preaching to the choir.