The actual length of each Spartan race varies depending on which location you pick to participate. But, they mostly hover in the 4-5 mile range which means they're meant do be done as an all-out sprint rather than a long, drawn-out slog. The Spartan organizers manage to pack a lot of pain into those few miles, though, relying on the element of surprise and not disclosing the course map before you run the race. If you enjoy the torture that the Spartan Race offers, they also provide increasing levels of difficulty that you can subject yourself to. Tougher events include the Super Spartan, the Spartan Beast and ultimately the Spartan Death Race, which is held in Vermont and might actually kill you. Don't forget to sign the waiver.
Get more information at Spartanrace.com