Here's another public idea:

It needs to be a kinda cool evening, so you have a reason to cuddle up together. You might want to wrap a blanket around yourselves the first time, but when you get more daring, forget it.

He has to sit on the ground first, and you have to sit on his lap. You have to be wearing a skirt or dress, no undies.

Can you guess the next step? Yep, full penetration, front or rear, your choice.

Oh, and try not to moan or scream, okay? Unless you're watching a fireworks display or something - which is where we first did this