abandoned
barb
barbed
barbwire
barrier
blue
border
boundary
building
camp
crime
criminal
danger
detention
estonia
exterior
fence
fences
fort
freedom
guard
imprisonment
institution
jail
metal
military
no people
observation
old
outdoor
penalty
prison
protection
punishment
razor
rusty
security
sky
soviet
state
steel
structure
surveillance
system
tower
wall
watch
watchtower
wire