1. to climb to the rear (Technically, it can mean that, but I doubt you'll see it in real life any time soon. Maybe for climbing to the backseat of a car from the front.)
2. to understand something ("dahintersteigen" - the "da" often gets split off and moved elsewhere. Pretty similar to "durchsteigen", but this one is more about one particular "mystery". Think of a magical trick that you can't understand how it's done.)