Walk on the Beach
This makes an excellent date because it can be as long or as short as needed. If it's a first date, don't make it too far, strenuous, or secluded and make sure you time it right so that you're hitting the sunset toward the end of the walk, not the beginning. A nighttime beach walk gets creepy quickly.
However, if it's not a first date, a nighttime beach walk is sexy as hell, and as long as the mutual attraction is there, you will definitely make out in the moonlight. It's nearly foolproof.