Basically, Sam and Dean having a lot of sexy sex in the BatCave, but in all random places. So, like, Dean drinks his coffee while watching Sam swim laps in the Olympic-sized pool. And then Dean gets beef from the meat locker. And then, they look at stars in the observatory. Maybe they pretend to be Katniss and use the archery range. Perhaps there's a room just for breaking dishes! Definitely there has to be a movie theater. What about a bowling alley? An armory? Full Catholic church, complete with priest and holy-water-to-go?
Possibilities are ENDLESS.
What do you want there to be?