The exterior of Mayfield Psychiatric Hospital was seen briefly near the end of the season 5 finale Both Sides Now. House realized how serious his Vicodin addiction really was, when he realized he had never slept with Cuddy nor had he detoxed at all. Then he and Cuddy went to see Wilson. Afterwards, intercut with Cameron and Chase's wedding, we see House and Wilson go to Mayfield Psychiatric Hospital. House, carrying a suitcase, goes in willingly without saying anything to Wilson.
Mayfield Psychiatric Hospital is going to be a major location during Season 6.