Tenzing is a sherpa living in the house just west of Burthorpe. The player needs to go through his house to take the secret path past Death Plateau on the way to Trollheim.
He is involved in the Death Plateau and Troll Romance quests. He sells climbing boots for 12 coins each.
To get to him, follow the path north of the Warriors' Guild then go west once there's a fork in the path. Continue up to reach the house. Open the gate, knock on the door and talk to him (you must have completed Death Plateau to equip these boots).