What is there to do in Mexico?

I'm 17 and my sister is 19. We're going to Mexico on friday for 2 weeks and was wondering if anyone had any reccomendations of what to do there? I defs want to swim with dolphins but was looking to see if there was anything else that would be fun or any ideas for a nice day out. We're staying in Playa Del Carmen, which is just below Cancun a bit.. so prob gunna go there for a night. But we've got 14days to fill and was just seeing if anyone else has been before and done any worth reccomending. Thanks :)