does anyone know where the key is ?

It's a guild locked dungeon, you need to join the College of WInterhold. Stupid, if you ask me.

damn i gotta go back to college?...my student loan is gonna be huge

All the College asks is that you share your findings with the brothers.

This. Guild locked dungeons is a bad idea, it's worse when they have shouts in them.

I was really disappointed that a key is needed to get into Saarthal. It's one of the weaknesses of the game, in my opinion -- interlocking quests.

I had a character that "needed" to get into Saarthal, and looked all around for the key. Then he finds out he has to join the College. This character was a Nord warrior and didn't want to have anything to do with those twerps in the college (his view not mine). So he had to leave a quest finished after already doing a lot of work on it.

One of my few comlaints.