The Feel of Sun on Naked Flesh
Re-create it inside: Do it in front of the fire. Pretend you're stars of one of those cheesy 80s movies: First you'd see a bra flung on a chair, then a pair of high heels, then two half-drunk glasses of champagne. Then, finally, a couple making out on a deep sheepskin rug, fire sparkling prettily in the background. Yes, it sounds cheesy, but anyone who's tried it has to admit it feels extraordinary! There's a reason why those thick carpets were called "shag-pile." People spent more time lying on them than walking on them because they felt so damn comfortable. Besides, firelight is massively flattering, and being naked in front of a fire, terribly decadent. Anyone for a martini?
Water or Beach Sex
Re-create it inside: Solo, use a hose showerhead attachment and direct the flow of water where you need it most. Try changing the water temperature (hot to cold) and strength (hard and fast to a teasing dribble) for variety. Sex in the bath or shower might not rival sex on a beach, but it comes in a sexy second place. In the shower, lean back on the wall, one leg raised high, the other on the floor for balance. He supports your raised leg with his hand.
At One with Nature
Re-create it inside: Go outside when it rains, jump around like kids until you're thoroughly drenched, then go inside and have sex in the shower or the bathtub. Alternatively, pitch a tent in your yard (if you're childless, do it under cover of darkness, and if the neighbors ask about the tent, say your niece and nephew were visiting).
On Vacation Somewhere Exclusive and Expensive
Re-create it inside: If you've got some cash to spare, take yourselves out to a ritzy hotel bar or restaurant, wine and dine, then search till you find relatively private/quiet bathrooms where you can hide for a quick five minutes. If money is tight, buy one of two indulgent treats you wouldn't normally spend money on (such as gourmet chocolate, expensive wine, a rich chocolate cake, organic strawberries), climb into bed and feed each other. Feeling spoiled and removed from the "everyday" evokes the same feelings.