The Tantalus V. Observatory is South Park's planetarium. It was featured in the Season Two episode, "Roger Ebert Should Lay off the Fatty Foods".
Background
Mr. Garrison takes the class on a field trip to learn about the stars and the solar system. The planetarium also hosts laser light shows set to the music of Kenny Loggins on the weekends.
Dr. Adams
Since the planetarium sees very little business, the doctor has resorted to using the laser effects to hypnotize students into becoming obsessed with the planetarium and working for free. He mentions a bone marrow disease, which causes a peculiar speech impediment that does not allow the him to pronounce the "t" in planetarium, making it sound like plane-arium.
The doctor hypnotizes Stan Marsh, Kyle Broflovski, Mr. Mackey, Nurse Gollum, and Officer Barbrady, who was brainwashed into thinking he is Elvis Presley, in an attempt to make them forget how the planetarium was hypnotizing people. The star projector was ultimately destroyed by Eric Cartman in a rage of anger that his friends were not supportive in his Cheesy Poofs commercial appearance, thus breaking the hypnotic power and caused the projectors lights to be beamed directly into Dr. Adams eyes, putting him in a permanent vegetative state.