There aren't any. The game isn't really the biggest in the entire GTA history, so there aren't really that many easter eggs or secrets.
There's only one easter egg I know of and it is very minor, there's a "HERE BE DRAGONS" written in the middle of the ocean.
What about radioactive waste, abandoned hospital,etc :D
Look at it now, take back those words! :P
Well, I never played it, but it would be nice if there was any myths on it. I can't tell if there are any because I never played it.