Trepanation is a procedure where a hole is drilled into the skull, exposing the dura mater and brain for either medical (releif of pressure) or mystical (supposed heightened consciousness)purposes. It is likely the oldest procedure in neurosurgery and has been practiced by many ancient peoples all over the world.
I would say ‘don’t try this at home,’ but it looks like modern-day elective trepanation is already a fad in communities which embrace extreme body modification. I assume I don’t need to say it, but I will anyway: drilling into your skull at home is a really really bad idea. (Unless of course you are trying to rid your brain of the secret pattern of “pi” which is driving you insane. Then its ok.)
To learn more about trepanning, check out Mo’s excellent post on the topic.