Try to scale the wall.

You have not been idle the past month, you have explored the area surrounding the colony and looted what supplies you could find after 21 years with most of the human race dead. One thing you did find was a set of climbing equipment with an Aluminum grappling hook. You wait for daybreak, shivering even through your nylon jacket and wool pants, then wait some more till a patrol comes across the section of wall you are watching through your binoculars you took from an old military hummer. When you are certain they are out of earshot you run up to the wall made of cinder block, mortar, brick and sheet steel and throw your grappling hook and chain over, then pull to seat it.

Monkey like you scale the fortified perimeter, and in a trice are over the parapet. Grabbing your chain and hook you make your way down the other side and sprint across the terraced hillsides towards town: your next destination being in that direction, no matter what you decide.