The simplest penetrations are much like swimthrough holes in the reefs, not much to fear there, the only real added danger is tetanus if you cut yourself on the old corroded metal. That said my first penetration dive included a 30m+ swim through the crew quarters of the Zenobia, there were frequent window ports large enough to let a diver out though, the entire area had natural light, and there was no silting.Wreck--They're all over, but even the PADI Wreck Course is only an intro. I took that but wouldn't do anything but the simplest penetration (and haven't done that). Much of the other info. is just common sense, but still informative.