army
barb
barbed
barbwire
barrier
black
border
boundary
building
camp
cell
concept
crime
criminal
danger
escape
exterior
facility
fence
freedom
guard
imprisonment
iron
jail
justice
law
metal
military
observation
old
penitentiary
prison
prisoner
protection
punishment
safety
security
sky
steel
structure
symbol
tower
wall
war
watchtower
wire