Located on the slope of Mt. Parnassus, for 10 points, identify this Greek city home to a famous oracle.
Supposedly this location produces gases from the ground with a high ethylene content, and this location was never visited during the winter months. One temple here was the Altar of the Chians, and other recognizable features are the Tholos dedicated to Athena Pronaia and the (*) Castalian Spring. This location was supposedly the site of the  slaying of the Python, and it is home to the omphalos which marked the center of the world. Located on the slope of Mt. Parnassus, for 10 points, identify this Greek city home to a famous oracle.
Supposedly this location produces gases from the ground with a high ethylene content, and this location was never visited during the winter months.
Delphi