Hey guys. I've killed the big hand guardian, I don't remember if he dropped a key or anything but the entire map is revealed except the tower part and I cannot enter.
Have I missed anything?
Thanks.

The hand guardian is the 6th boss, Gauntlik. You have yet another guardian to defeat who's in the Halls and yes, you require a key that Gauntlik will drop. Go back to where you defeated him and check if it's still if it isn't already in your inventory. Last it could be in another place but I don't want to spoil more unless that's okay.