Coral reefs aren't the only places to dive. There are many spectacular places to dive where there are no reef-building corals. Some of them require specialty certifications and extra precautions, but others can be enjoyed with nothing more than an open-water certification, and a few are accessible to free diving and snorkeling.

• Kelp forest: Kelp are large seaweed that thrive in underwater forests in cool, temperate waters. Gliding through these towering giants, in a cathedral-like atmosphere with long shafts of light flickering through the long and sinuous leaves, or fronds, is an experience you never forget. The Monterey area, in northern California, and the Channel Islands in Southern California, are some of the best places to dive in a kelp forest. Water temperate in the kelp forest usually hovers in the 60s in summer, dropping into the 50s in winter. A heavy wetsuit or a dry suit is required. Winter can bring rough water and heavy surf, but sometimes better visibility. Average visibility is about 60 feet, but it can be much less.
• Wrecks: Wrecks have their own undeniable fascination. There is something compelling about swimming over or through the sunken endeavors of other human beings. War wrecks are probably the most compelling of all, and the western Pacific has an abundance of them.
• Artificial reefs: Artificial reefs are a relatively new idea. Essentially, they are sunken wrecks -- obsolete ships or planes -- purposely sunken to attract marine life and divers. The southeast coast of Florida has a number of these sunken artifacts. A number of ships have been scuttled off British Columbia, along with one in the Cayman Islands, and more are planned.
• Cenotes: On the Yucatan peninsula, as in many low-lying tropical areas, the bedrock is limestone, the remains of ancient coral reefs. This limestone is often riddled with caves, and the caves are frequently flooded with groundwater. In places, there are vertical shafts that extend to the surface; in other areas, the ceilings of these subterranean caverns may collapse to form cenotes (see-NO-tays). These sunken ponds are often connected to enormous labyrinths of submarine caves filled with lots of spooky and wonderful formations such as stalactites, stalagmites, and flowstone.
• Freshwater: Cenotes aren't the only kind of freshwater environment where you can dive. Lots of divers explore lakes, sunken quarries, rivers, and other freshwater environments -- there are undoubtedly those who have never dived in ocean water at all. A cubic foot of freshwater weighs a little more than 62 pounds, while the same amount of seawater weighs 64 pounds due to all the dissolved salts. What it means is you won't need quite as much weight when diving in freshwater as you do in saltwater.