If you're determined and quick enough to pass the '??' rated Dreggs at the end of the Grotto, you'll come across an interesting Hive base. Additionally, there is an enemy there known as the 'Shrieker.' I scoped it out from afar and it's pretty out-there. I won't ruin it for you with a picture, but you should absolutely check it out before the end of the beta. Exploring like this is one of my favorite aspects of Destiny. Can't wait to see what else we'll find.