There where of course other impressive buildings in Athens during the classical period than the ones at the Acropolis cliff. This is one of the best preserved, the temple of Hephaistos and Athena at the edge of the Agora on the Kolonos Agoraios hill. Notice that it's sometimes called Theseum after the friezes depicting the deeds of this Athenian heo - most of the pieces depicts the labours of hercules though, buy they are badly worn down by time.
Anyway, as a quick summery, this is a classical temple in the Doric order, constructed between the 450's and 415 Bc. The long construction time may be due to a number of reasons such as more or less constant warfare and that the Parthenon was prioritized. Yet, this was an important project as we can guess by the fact that the temple was built almost completely in marble and that the cult statues (Hephastios and Athena) was made by Alkmenes, a pupil of Phidias(who made the great Athena in the Parthenon) between 421 and 415 Bc.