From the Fields of Misery you need to go to the Drowned Temple to follow the Broken Blade quest chain. If you don't know where the Drowned Temple location is, go the the north east of the Fields of Misery until you meet a band of thieves. When you reach the Drowned Temple, an ancient guard will meet you and will tell you that you need to go to the Festering Woods to collect the Beacon of Honor and the Beacon of Light. In the same region you will have a nice event called the Memorial Stone where you need to play a little "king of the hill" with some spirits.
After this you need to go back to the Drowned Temple and put the two Beacons in place in order to be granted passage by the guardian. Before you enter the temple, he will warn you that his brethren will try to harm you. On the normal difficulty it is quite easy inside the temple, but I bet later on, it will become very hard. You can see the exact location of the Drowned Temple in one of the two pics bellow.
I hope this post will help you find the entrance of the Drowned Temple in Diablo 3.