Otter
One of the greatest things to do in this country no one knows about!
the incredible people at Tranquility Bay have come up with something really cool. TB Is actually IN a marine reserve, so they will put you on a small boat, dock you and Mrs Otter at the reef, and they Kayak you each course of your meal.
They are booked for V day, but if you book a night there, and reserve the boat for a dinner, you can give her a gift cert or something to show her what she's getting. SUPER romantic.
OR...you could go to Hidden Valley Inn and reserve their Private Water fall for the day (you'd also stay the night in a luxury cabana) if you wanted
Romance...ah....belize!