We use taxis. The main reason being the resorts are often set back from the main road, so walking out of the resort to the nearest bus stop can easily take 20-30 minutes, which is not my idea of fun in the Mexican heat! The hotel will call a taxi for you, no need to pre-book, they have them waiting all the time. A taxi into Puerto Morelos (a small fishing town that we like to visit to do our shopping and have lunch; if you’re into snorkelling or diving I’d suggest going with one of the several dive shops there) costs approx 150 pesos/15 USD, and a taxi into Playa del Carmen costs approx 220 pesos/22 USD, each way.
They do also have an ADO bus system (large air conditioned coaches) which are reasonably priced and we spoke to a few people who visited the ruins on these rather than taking an escorted tour from the hotel (it works out much cheaper).
The trips and activities we’ve done over the last 3 years are:
Speed boat and ATV combo at Maroma beach, which was great fun (half day trip, cost approx 65/70 USD pp if you shared vehicles if I remember right)
Selvatcia: zipline park which was great fun. Costs approx 100 USD with transport. Xplor is also highly recommended and there’s more to do there, so worth a look if you’re into that kind of thing
Crococun Zoo near Puerto Morelos: you get to interact with and touch/hold/feed different animals inc baby crocodiles/crocodiles, deer, parrots, snakes, Mexican hairless dogs, and spidermonkeys (there are wild ones which are so cool as well as some which they rehabilitate)
Resort course dive: most resorts offer these, you have basic training in the pool and then do a shallow open dive, again, great fun
Snorkelling: we did this through a dive shop in Puerto Morelos. We paid about 13 USD pp for 1.5 hours just us two with our own guide. If you head to Akumal, you can snorkel with turtles, though I haven’t done this myself, it’s highly recommended
Chichen Itza: large site, approx 3/3.5 hours away. Very interesting. We also swam in a cenote which was absolutely beautiful and stopped in Valladolid (colonial town) for about 30 mins)
Coba: we did this with a company called All Tournative and would recommend it. Coba itself is pretty cool, and situated in the jungle; when we were there we were able to climb it, I’m not sure if this is still the case. Also included on the trip was rappelling down into a cenote, zipling back across, canoeing down a small (and very shallow!) river to the jungle, walking through for approx 5 minutes looking at pretty birds and wild monkeys, witnessing a Mayan ceremony, then swimming in a cenote. Great fun. There’s a photographer with you all day (very unobtrusive) so you can purchase photos on a disc as a memento.
Tulum: the setting is pituresque on a wonderful beach, but it was our least favourite ruin. The site is very open and VERY hot, with little shade, and we just didn’t find it as interesting as the other two. But, at approx 20 minutes away, it’s the closest and so popular for that reason
There’s a wealth of other trips available inc Xel-ha and Xcaret which are popular but have never appealed to us, cruises (eg a lobster cruise from Cancun), and so on. I’d also suggest getting a honeymoon photo shoot done; we’ve had photos done at the Excellence in Mexico and the Bahia Principe in the DR, most resorts offer this (I’m pretty sure the VIM do, but contact them to find out) and it makes a lovely souvenir IMPO.