“Unlimited” admission means that for the period of validity of the pass, the holder may visit as many times as desired.
“Free” admission means that for the period of validity of the pass, any given visit requires no additional payment of an admission fee.
A pass that offers “free” admission may be good for a fixed period, or for a specified number of visits, whichever occurs first.
A pass that offers “unlimited” admission for a fixed period may require a (discounted) payment for each admission.
A pass that offers “unlimited free” admission for a fixed period will not require payment for any admission within the period of validity, and the holder may visit as many times as desired within that period.