Welcome to the forum Andrea and Dave!!
Alright, non beach, non hotel. What about Xcaret??
Xcaret Weddings - Natural nuptials eco wedding Xcaret locations
They have a ton of wedding locations that are in the jungle, on ruins, in a church. And from what I've seen it's very beautiful. Plus, it's VERY close to a bunch of resorts in the Playa Del Carmen (and north) area so your guests could all stay at the all-inclusives, but have your wedding offsite!