The Oracles are beings and places that can give prophecies in Greek mythology. Four of them are associated with the god Apollo. There are five of them.

The Five Oracles

The Oracle of Delphi

Also known as the Pythia, she resides at Camp Half-Blood and gives prophecies to demigods who are about to go on quests. According to tradition, the questers are required to consult the Oracle. No prophecy, no quest. 

The Oracle of Cumæ

The author of the Sibylline Books.

The Oracle of Erythaea

Not much is known about this oracle.

The Oracle of Trophonius

This oracle is inhabited by the spirit of Apollo's demigod son Trophonius.

Grove of Dodona

The only oracle not affiliated with Apollo. it is sacred to the titan queen Rhea