Well I must suck because I'm dying like crazy. Guardians kill you instantly with their beam and avoiding it is basically impossible without cover. Those things are terrifying. I can't seem to do much of any damage to them so the best strategy so far seems to be to panic when hearing the sound effect cue that they're near and run like hell dodging and weaving until you're away. This is one dangerous overworld.
I did wander into Hyrule Castle which is apparently the final area in the whole game after an early quest objective sent me there to confront ganon. I quickly got trounced and had to turn back. But damn, that music.
Think Ocarina of Time's guards in the garden sneaking, except ten times more epic and dangerous scaling walls and avoiding detection by guardians. I guess you can apparently go straight to ganon if you're some kind of psycho gamer but I don't nearly have the ability to do that with only three hearts and few weapons so I had to turn back and pursue the main quest to get stronger.