Just a simple steel cable. Anchored to a high point and the other end anchor to another location lower and farther away. You can do anything from throw a thick leather belt strap over it to a chain or even a roller system with brakes and everything. Grab whatever you slung over that line with both hands, pick your feet up, and you'll go sliding down that mf cable so fast you better know when to let go and not crash Into whatever to anchored to down the line.