The challenge is that you have to be an experienced cacher who has found at least 1.000 caches with either D-rating or T-rating (or both) being 3,0 or higher.
Myself as owner I have fulfilled the requirement with 1.280 qualified caches found (as of Jan 07, 2017).
The D-rating of this challenge refers to the requirement, the T-rating refers to the actual hide-out.
Who wants to avoid pathless hiking between Level 2,5 and Level 3,0 can use the additional waypoints from the listing of level 2,5.