How about climbing? I may be crazy but I love climbing. Not only is it a test of fitness, but also of persistence. I'm not a big fan of "stand and mash" as that is very hard on your knees.

• I'm not afraid to use my low gears as much as needed. Save your standing climbs for a final push over an obstacle, around a switchback, a short steep section, or to crest a rise. Standing is ineffective for long, steady climbs.
• For effective climbing, depending on the grade, stay seated, get a good leg extension, and set a pace that you can maintain. Try and save one last gear in case you need it. For steeper climbs, or getting over an obstacle while going, get forward. Get so far forward that the nose of your saddle is poking you in the butt, and put your chest down to the handle bars, and maintain your momentum. Use a little body language and momentum to get up and over whatever it is. Also, try and keep the front of the bike stable, pull back and down gently on your grip if it seems like your bike is wandering all over the trail.
• If you have a lot of trouble climbing, if it seems like you are having a hard time finding your center, or that the front end of the bike seems too light or is bouncing all over the place, here are some things to check. First, have the fit of your bike checked, specifically the cockpit length. If your bike is too big, you may have problems here. Second, is your front fork a) a piece of junk that needs replacing or b) locked out and you forgot to turn it back on? I do that all the time.

Article Credited to: Formica