There are a lot of EXTREME / Ultimate multi-challenge endurance kinds of races out there. Some might consider 3 Gun in that group as well, although most of the 3 Gun courses are more sprint like.
With Tough Mudders, IronMan Tris, Ultimate Marathons, and Spartan Challenges, I have now seen a new one… The Train to Hunt series of races. This one is pretty hardcore.
And of course the 24hr Sniper Challenge craziness. Challenging courses, that will definitely leave you with a sense of accomplishment when you finish. I think I will stick with the short course events in 3 gun though.