Sam and Dean haven't had a case in a week or so, and they find themselves in Oregon, just wishing for a case. When they hear of Gravity Falls, it seems like a cheesy enough tourist trap to relax for a bit in, but the town turns out to be so much more, and they realize they're not alone on their new case when Mabel and Dipper Pines show up. (Spoilers for Se.8 of SPN and ep.17 of GF)

They've seen it all. Vampires, ghosts, demons; if you can name it, they've likely encountered it. But no experience could have prepared Sam and Dean Winchester for the oddities of Gravity Falls. And yet, for Mabel and Dipper, it's just another summer's day.