A beautiful and intimate beach with white sand, gorgeous light house, and nature trail. It costs a couple of dollars per vehicle to enter but so worth it! I advise going during a weekday.
Walk around the downtown Coconut Grove strip! If you go early, you can enjoy shopping at their variety of stores, have brunch at Greenstreet Cafe, or browse their local bookstore Books & Books. If you go at night, enjoy a fancy dinner at one of the Grove's most scenic outdoor restaurants, Glass & Vine, and afterwards take a stroll along diner key marina. For a /really/ late night, enjoy stand-up comedy at the intimate whiskey house that is Taurus- where the bride had bartended once upon a time.
Take a stroll along Miracle Mile! Although the Umbrella Sky Project is no longer there, you can enjoy the beautiful walkable architecture of Giralda Plaza and if you are hungry, you can take your pick at a large variety of cuisine- from Thai to Spanish to Mediterranean to Irish- there is a lot!
Replicate one of Sawyer and I's favorite date nights: watch an indie film at the Coral Gables Art Cinema and then walk to Books & Books across the street for live music & drinks!
Double Museum Date! If you're a museum nerd, this is the perfect idea for you. Visit the FROST Science Museum and then walk a few feet to the Perez Art Museum for an evening of modern art! The walk to and from museums is as scenic as it gets. Tip: On the second Saturday of the month, the Perez Art Museum is free (although packed!). Every 1st and 3rd Friday of the month (I believe) the FROST Science Museum hosts a laser light-show in their Planetarium, usually throwing it back to rock and roll classics but also sprinkling in Lady Gaga and Madonna too every now and then! I recommend visiting their websites for tickets.