Prison

A prison is a government-run facility where inmates are forcibly confined.

Known Prisons

 * Ravencroft Institute for the Criminally Insane: A prison for those not mentally fit for regular prisons. Located near New York City.
 * Ryker's Island. Handles normal prisons. Located near New York City in the East River between Queens and the Bronx.
 * S.H.I.E.L.D. Helicarrier: The floating headquarters for S.H.I.E.L.D. has a prison facility for criminals they don't want the world to know about.
 * Vault: A prison for enhanced supervillains.

History
Beast was in prison following an attack on a government facility. Magneto tried to break him out but Beast refused.

Puppet Master tried to use the inmates of a prison to take over the world.

The Fantastic Four were held in a prison after Skrulls impersonated them and attacked others.

Iron Man broke into the Vault to disable those using his technology and was confronted by Hawkeye.

Kingpin broke several supervillains out of a prison to form the Insidious Six.

John Hardesky was held in the S.H.I.E.L.D. helicarrier's prison facility.

Background
It is possible, though unspecified, that the prison seen in the episodes  and  are Ryker's Island.