The Mt Rainier Infinity Loop is an unusual challenged dreamed up by iconic Washington climber Chad Kellogg, but which he was never able to complete due to his untimely passing. The idea is to:
-Ascend Rainier and then descend by a different route approximately on the other side of the mountain. For example, starting at Paradise, ascend Disappointment Cleaver and descend Emmons Glacier.
-Run the Wonderland Trail back to the starting point.
-Repeat the ascent & descent.
-Run the Wonderland Trail the other direction back to the starting point.
It works out to 130 miles or so, with 40,000+ feet of elevation gain.