To unlock the following Orsinium DLC Trophies, complete the following tasks.

Trophy	How to unlock
Hero of Wrothgar (Gold)	Complete quests, defeat bosses, and explore delves to become the Hero of Wrothgar.
Kingmaker (Silver)	Complete Wrothgar's main quests.
Maelstrom Arena Champion (Bronze)	Conquer all challengers and earn the title of Maelstrom Arena Champion.
Maelstrom Arena Conqueror (Silver)	Conquer all challengers in Veteran Maelstrom Arena.
Wrothgar Adventurer (Bronze)	Complete 27 quests in Wrothgar.
Wrothgar Master Relic Hunter (Bronze)	Collect all 20 relics for the House of Orsimer Glories.