The area at Temple of Leto, a goddess who was in love with Zeus and triggered his wife, Hera, to be so angry Leto was fled to Delos when she was pregnant. There she gave birth to no less progeny than Apollo and Artemis. Their temples stand next to the temple of Leto, who was the most important here.
The temples were, according to an inscription, built by King Arbinas in the end of the 5th century. The Leto temple was used as an annex to a much later church, which was built using stones from the other two, of which much less remains.
The Leto one has the columns still standing, next to it is a smaller temple, greatly destroyed, of Artemis. The Apollo one is somewhat larger and slightly better preserved.