Why just run when you can also tackle obstacles???
Leave the mud for the warriors and tough mudders, here all you need is legitimate brawn and resilience... I introduce you to the great Urbanathlon, hosted by Men's Health Magazine.
10.2 miles of running broken up by some serious obstacle courses (marine hurdles, climbing under Jeeps, scaling buses, monkey bars, etc. etc.) and a fun after party with beer and music at Crissy Field (last year's race included free beers with registration)
2012 race details coming soon here: http://www.menshealthurbanathlon.com/san-francisco-course.html
Two options for participating - take it on solo or join forces in relay teams of 3. Please note in your RSVP if you'd like to form a team.