barbwire

barrier

bars

boundary

brick

cage

camp

captivity

cell

chain

circles

convict

crime

criminal

danger

defense

empty

enclosure

escape

exterior

facility

fence

forbidden

guard

imprisonment

iron

jail

jailhouse

justice

keep

metal

nobody

obstruction

old

penitentiary

prison

protect

protection

punishment

safety

secure

security

sentence

sharp

sky

steel

stone

trapped

wall

wire