Where we stayed
We stayed in a basic 1-bed apartment in the downtown area found on AirBnb for about $35/night. Hands down, the best thing about it was that it included two bikes (and locks). Biking was an awesome way to get around and was one of our favorite things to do in general. The apartment also included snorkel equipment (and the building had a very cute cat in it).
We preferred this over the "all inclusive" resorts so we could feel free to go out and explore and eat without feeling like we had to eat at the resort since we're paying for it.
What we did
Our main activity was diving with Aldora Divers. They're a bit pricier than other companies, but because they use larger steel tanks, the dives are long – each dive was 70-90 minutes, almost double the amount of time I've gotten out of other companies' tanks. We rented all our equipment from them and were happy with the quality and upkeep of everything. The guides really went above and beyond to take us to some awesome sites.
The diving was amazing. We saw incredible coral formations, turtles, all kinds of fish, huge Moray eels, octopus, pufferfish. We did a night dive in the dark, which was a little creepy at first, but turned out to be the highlight of the whole trip, because of all the weird cool creatures you can only see at night.
Honestly, diving/snorkeling are the main activities on the island. The beaches aren't great for lounging because most of them are rocky and reefy. In fact, most of the sandy beach areas you'll see are actually fake – they bring in the sand and dump it over the rocks.
All inclusive "beach clubs" are pretty popular for general lounging, eating/drinking, massages, snorkeling, etc. We spent two evenings at The Money Bar, eating and drinking and enjoying the sunset and the fun cover band. We liked this one because it's not actually "all-inclusive" like most of the others, you pay individually for each drink and food item. Since we aren't big drinkers, the all-inclusive entry fees are more than we'd otherwise spend. The Money Bar has a small pier/dock thing that was fun to sit on and jump into the ocean during the sunset. It was about a 10 minute taxi ride from downtown, near a lot of the other resorts and beach clubs.
Getting around via bikes was an activity in itself. We explored around town on bikes, and we even rode from downtown all the way south to the resort area. Lots of people ride scooters, and traffic is pretty slow-moving, so its comfortable riding bikes on the street in the downtown area. Once you get to the highway, there's a nice bike lane.
We really wanted to see Chichen Itza (ancient Mayan city site) so we took a day trip. To get there, we had to ferry to Playa Del Carmen and then take a bus to the ruins. It was a long day with a lot of traveling but completely worth it. The site was incredible and there was so much to explore beyond the big famous pyramid calendar. We learned about Mayan culture, beliefs, sports/games, science/math.
We used this site to book our tickets for the tour, which was $65/person. The place we stopped at for lunch was probably the best food we ate on the whole trip – it was in a small village and even though it was a buffet, the food was delicious and fresh and homemade. We also stopped at a cenote (underground water hole) and got to jump into it and swim which was very fun.
Typical for tours like this, there were so many times along the way where we were being sold extra stuff, which honestly did wear on us by the end of the day. Like I said, it was a very very long day, but we really wanted to see Chichen Itza and we're glad we did.
What we ate
Amparo's: Breakfast cafe with coffee, fancy juices and smoothies, and a lot of really awesome breakfast options. We ate breakfast here multiple days on our trip. We loved the smoothies, banana pancakes, huevos rancheros, eggs benedict (we asked for no ham and they offered to add sauteed mushrooms!)
El Palomar: Downtown restaurant in a stunning older building with some interesting food choices beyond just tacos and ceviche. Super fun place to sit and enjoy the downtown atmosphere and ocean views. Everything we got was delicious; the sopecitos were a fav.
Hemingway: More of a bar/lounge with food. It's right on the beach and a little out of the way from the middle of downtown, so it was less crowded. We loved sitting on the shaded patio and eating/drinking with the ocean view. There's also some nice little snorkel spots nearby.