It's hard to find a little bit of solace in Playa del Carmen's tourist mayhem, but if you leave Quinta Avenida behind and keep walking another 15 minutes or so south-west, you'll stumble across a small park with Mayan ruins.
The scale is of course nothing like Tulum, but the upside is that you won't have to share the Xaman-Ha ruins with hordes of other sightseers.
Just walk around and soak in a little of the ancient history. This is also a charming place to have a picnic, write a letter, or read a book.
A warm thank you:
My trip to Playa del Carmen was courtesy of Mahékal Beach Resort (http://www.mahekalbeachresort.com). The amazing folks at MedjetAssist (https://medjetassist.com) ensure that I take trips, not chances.