adj. 25B6; adjective
each site is unique : DISTINCTIVE, individual, special, idiosyncratic; single, sole, lone, unrepeated, unrepeatable, solitary, exclusive, rare, uncommon, unusual; informal one-off.
a unique insight into history : REMARKABLE, special, singular, noteworthy, notable, extraordinary; unequalled, unparalleled, unmatched, unsurpassed, incomparable; formal unexampled.
species unique to the island : PECULIAR, specific.