one place that is relatively deep and a shore dive is in the lower keys just below(heading south) Bahia Honda state park on the opposite side of the road. you can easily miss the turnoff to find it. the place is called "the horseshoe" because you can walk 3/4 of the way around it. it is where the dug out a lot of rock when they built US1 in the center its about 30 feet deep sort of like a minnie quarry. it is good for practicing your skills but not too much to see. I was there twice right after I was certified and used it to practice buoyancy skills and get used to some new equipment with my dive buddy. there was a few bigger fish but mostly small fish and very (corral) rocky when entering and exiting the water. It is a free place to get wet and some locals do hang out here in the shade drink beer and fish the outside of the horseshoe. when you pull in you will see a long driveway go to the end and a short path leads out to the "horseshoe" Bahia Honda is also a really great park with super nice beaches.