The best thing about "secret" hotels is that you save huge amounts of cash on a luxury break. Rather than be left with empty rooms in quiet times, these hotels offer reduced rates through online travel agents, but they keep the exact location secret until you've booked. You can get a seriously great deal, and the surprise just adds to the fun. Check out Lastminute.com's Top Secret Hotels, Secret Escapes, and Late Rooms for the best deals.
Top tip: Pay close attention to the images of the rooms; if you've been looking through a lot of hotel websites, you'll be able to recognise some of them and nab the one you really want. You can also get lucky by googling the hotel description.