So you've foolishly lashed out on a spa deal coupon and then realised there's no way you're trekking into bland suburbia to fulfil it. Swapdeals lets you list it for a possible trade or sale to other bargain hunters.
You can elect to swap your deal for another of similar value, or offer a cash price. You're unlikely to make a sale if you ask for more than what you originally paid, and I suspect you'll do better if you ask for a little less.
The main caveat is to be sure that the deal site you've purchased your original deal from allows deals to be passed on to others. (Many do, since buying experiences as a gift isn't uncommon.) Right now there's not a lot of volume on the site, but to be fair it has only just launched.
Swapdeals is free to use, requires registration. If you've tried it out, tell us about it in the comments.