For two adults traveling alone I would definitely recommend a visit to Epcot. It is a huge park with a ton of sights to see, attractions to experience, and places to explore. Start your day off in the front of the park, at Future World. Be sure to head to Soarin' as it is an attraction that should not be missed. The Living with the Land boat ride in that same pavilion is a favorite of my husband and I, though our kids aren't as thrilled with it. Take some time to look around the rest of Future World, including
Innoventions and Test Track. Once you've had your fill, make your way back to the World Showcase section of the park, possibly stopping for lunch at Cantina de San Angel, a quick service eatery. You could even grab a margarita from the outdoor stand. Spend the afternoon strolling through the unique pavilions that represent various countries from around the world and make up the World Showcase. There are great snacks to try and quaint shops to poke around in; it's a very "wordly" experience. Close out your day with a meal at Tutto Italia or Le Cellier and then pick up a pastry from the French bakery to enjoy while you watch Illuminations.
If you have another day, I'd opt to visit the Magic Kingdom as it offers the quintessential Disney experience for both the young and the young at heart. The attractions there are second to none when it comes to bringing magic to life. Even a stroll down Main Street, USA will make you feel like a kid again. And don't skip Fantasyland; the attractions there will surely bring back memories from when you were a child! Liberty Tree Tavern is a great spot to grab a hearty lunch. And the ice cream cookie sandwiches at Sleepy Hollow are DE-licious!
Enjoy your visit!