  Entanglement entropy is one of the most prominent measures in quantum
physics. We show that it has an interesting ergotropic interpretation in terms
of unitarily extracted work. It determines how much energy one can extract from
a source of pure unknown states by applying unitary operations when only local
measurements can be performed to characterize this source. Additionally,
entanglement entropy sets a limit on the minimal temperature to which these
partially characterized states can be cooled down, by using only unitary
operations.
