Any diving when there is a "ceiling", that is a physical or logical barrier that blocks the diver from unimpeded access to the surface, the risk factor and level of training required increases. Physical barriers are caves, wrecks, and things like submerged buildings. Logical is a decompression requirement. Both types can apply to the same dive.
Wreck diving training covers how to negotiate tight places safely, run a line to the entrance, work with your buddy, finning techniques that minimize kicking up silt, and a lot more.
Divers without this training can still enjoy wrecks from the outside, no penetrations allowed, as long as they stay within their other limits such as depth.
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I am not the one who needs mental help. I just need to vent. | 
On television you can watch wreck divers.... 
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