Spontaneity is a wonderful thing if you plan it well and your lover will cooperate with you on it. A romantic getaway is most often something that two people plan, but if they trust one another, one person might spring a getaway on the other during a day off. This has risk, but the reward of doing it might be stunning.
"We leave tomorrow" means "I have planned something fun. Trust me and go along with it." If initial shock leads to trust, the thing had better work. Expect questions, but the fun of this involves withholding some of the answers. Be prepared to say how long you will be gone, what amount and type of clothes and necessities to pack, the travel time, and what is the mode of transportation. But, resist the "where are we going" questions by saying that you have found a Shangri-La and it will be best served as a surprise.
Assuming that you know your lover's delights, and they are available at your shared destination, book some of them ahead, leaving yourself the option to shift the time. If your honey is adventurous, plan action events. If studious, plan interesting side trips. If you want to leave the world behind, plan seclusion. If you are wise, you will schedule some of all of these things, for a diversity of experiences that will make your Shangri-La memorable.
My love appreciates seeing something new, a little shopping, a scrumptious breakfast while enjoying a stunning sunrise, flavorful coffee, a sissy cocktail by the pool, boiled peanuts at the beach, a light massage, a shaded balcony with an ocean view where she can read some of her current favorite romance novel while sipping a wine spritzer, a romantic dinner, some slow dancing, and a nice room at the end of it all where we can rediscover why we like each other. The cell phones, the television, and maybe the music get turned off. This is a getaway from all of that. It is a date.