On Carol's birthday, the family plus one boyfriend (Rachel's) went to the Sandy Spring Adventure Park. (click to embiggen the pictures)
The safety system is immensely clever; at all times you are connected to an anchored steel cable by at least one cable hooked to your harness, and at most times two cables. You cannot remove both cables at once until you're safely on the ground. I was not once concerned about falling and at one point when Ben was stuck about forty feet off the ground, there was more concern about getting him through a tough spot than worry that he would fall.
The zip lines were great fun.
It's a good workout and requires some problem solving skills. We had a great time.