The Bone Pit is received in Act 1 if you complete the quest Birthright. There are two slightly different versions depending on who helped Hawke getting into Kirkwall during The Destruction of Lothering.
If Hawke sided with Athenril...
I've got a lead for you. A merchant I acquire goods for told me that workers have gone missing from his Bone Pit mining operation. He mentioned that the missing miners were Fereldan, which made me think of you.
If you're interested, go hit up Hubert in the Hightown Market.
If Hawke sided with Meeran...
If you're looking for work, there's a rich merchant in Hightown who's got trouble with his mining operation. If you haven't heard of the Bone Pit, the locals say it's cursed. I don't put much stock in it, but I had to turn down the job because of Marchers in my crew making the rest superstitious.
Go speak to Hubert Bartiere in the Hightown Market if you're interested.