Tranquillum House is fictional, but it is filmed at a real wellness retreat in each season. Season 1 used Soma Byron Bay in northern New South Wales, Australia. Season 2 moved to the Austrian Alps. Both are bookable. Here is what each one is, what they cost, and how to book.
Retreats are the easy case, because they want the attention. The harder ones are the hotels that carry a film they never asked for, and the clearest example is the Overlook, which was two separate buildings rather than one, with only a single one of them taking guests. I explain which hotel is which, and what a night at each costs, in the Shining hotel, Stanley and Timberline.