Great one hour boat cruise on the Key Largo Bay side. Cruise says up to 6 people and we showed up same time as two other couples traveling together. Owners promised a great experience and they delivered. We actually went out on a private boat with our Captain Bruce, while the owner Captain Kevin took the other group.
Bruce was very informative, pointing out big time private residences like Pitbull's home and Bayside bars like the Caribbean Club and Jimmy Johnson's Big Chill where he's worked before.
We talked about the manatee and dolphins in the bay but didn't get to see any. He also explained the the bay had an average depth of only 7' and we could look down and see the bottom.
I'd highly recommend this excursion early in your trip as these guides do a fantastic job of explaining all there is to explore in the Key Largo area.