For this Achievement, you need to collect 20 Relicts for the House of Orsimer Glories in Orsinium. The House of Orsimer Glories is a museum found in the city of Orsinium.
You can check which Relicts you already have collected.
In the
menu go to:
Journal/Achievements/DLC/Orsinium/Wrothgar Relic Hunter
Here is a link to a written guide and a Video below:
http://forums.elderscrollsonline.com/en/discussion/230894/wr... Credit for the video goes to Saturn666