The swirling decorative features of the column capitals are called volutes, a hallmark of the Ionic order. Note how on the corner, where two meet, they protrude.
Compare to the Erechtheum on the Acropolis of Athens: Erechtheum Porch.
Note how this arrangement makes the volutes in the Temple of Apollo at Bassae unusual: Temple of Apollo at Bassae (i.e. all the volutes protrude).
Ionic Frontage
The building has an octostyle (8 column) frontage (like the Parthenon, although its cigar-shaped columns belong to the Doric order).