The Temple of Hephaestus, also known as the Theseum, is a well-preserved ancient Greek temple located in Athens, Greece. It is one of the best examples of the Doric order of Greek architecture. The temple was dedicated to Hephaestus, the ancient Greek god of metalworking and fire. It was built around 449 BCE and is one of the few ancient Greek temples to have survived largely intact.

The temple was constructed using marble and stood on a raised platform surrounded by columns. It originally consisted of a cella, or central chamber, surrounded by columns and an outer colonnade. Today, many of the columns and part of the entablature are still standing, allowing visitors to get a sense of the grandeur of the ancient temple.

Over the centuries, the temple has been used for various purposes. During the Roman period, it was converted into a church dedicated to St. George. In the 19th century, the site was excavated and restored, and today it is one of the most popular tourist destinations in Athens. Visitors can tour the site and see the remaining columns, as well as admire the views of the city from the raised platform on which the temple stood.