Are all the sites/ruins etc... attached to quests? If i just go walkling around and exploring, clearing places, could I possibly break a quest that I have not yet acquired? Thanks.

Ha, not even close. I'd say over 90% of locations in the game are entirely optional.

There are some that are linked to quests, but those come in two categories.

1. You do a dungeon and get the quest item, and it sits in your inventory till you get the quest.
2. A dungeon is linked to a quest, and you can't enter it without getting the quest.

So, play on and enjoy.

PS: You can't remove quest items from your inventory.

PPS: I've completed about 50-60 dungeons since release, only two I couldn't get in without the quest. One is a large area that connects a group of dwemer dungeons, and also requires a quest to open it up.

Great, thanks!