One image I've felt to be intriguing since I was a kid - I don't think I'd seen it in this form, it just entered my mind, so it's an early bdsm fantasy - could be used in a countryside setting:

The captive/slave is brought to a house with a water mill, and a powerful upright wheel (of at least six-seven feet radius), the classic kind that's got a brook running down over it and into a millpond. He/she gets hands tied at the back, is gagged, knees and feet are bound and then the feet are secured by a strong chain to one of the "shelves" of the water wheel, so hanging bolt upside down from this shelf and trailed along as the wheel is moving round and round, constantly with the head downwards and dunked into the water once for each turn of the wheel. Wonderful!

Of course, this presupposes first, that the water can be led off and the wheel stayed long enough to fasten the slave to it, and second, that this slave has some sort of protection for his/her head. And you couldn't remotely do it for more than an hour, not even in a story where it's OK to stretch the physical limits a bit. Of course the wheel doesn't go so deep into the pond that the victim would get under for half the time or more in every lap, let's say it goes two feet deep, that's just enough.