[kaybe]

So... if I buy the land I need, can I just build a bridge over a river or do I need some kind of special permit? (Small streams are obviously ok since that is done a lot.)

[AstralStorm]

You might need city architect permit or equivalent and have to employ certified civil engineers by law.

[dsfyu404ed]

If your government respects personal property you can generally do what you want on your own land without permits as long as you don't make a business out of it.