The Kidnapping
Idea sent by SeleneDeTracia.
The idea is to send a note to your partner's workplace (or home, if they don't work) on a day they think you won't be able to see each other for any reason. The note should be written as if it came from a secret admirer, without detailing who might have written it, and trying to create as much suspense as possible. The content of the note will cover what is outlined below:
At the end of their work shift, you need to arrive without them noticing and blindfold them with a silk scarf by surprise, whispering something sweet in their ear so they know it's you. Tell them they're about to experience their own personal kidnapping and that there's nothing they can do to avoid it (you can invent an original motive for the kidnapping if you want).
From this point, there are several options: you can take your 'hostage' home where you've prepared a romantic dinner or to a beautiful spot for a picnic. Regardless of the chosen location, the kidnapped person will have to pay a ransom (imposed by you, hehe) if they want to be released, and of course, they can't leave at any time (although in the end, they'll surely not want to!... things of the Stockholm syndrome ;)). It's important not to remove the blindfold until you reach the planned spot.
The small details needed to round off the idea are up to you. Happy kidnapping!