Well, since you asked…..
As a professional traveller, who visits 2-3 different long haul destinations each month and have done for nearly quarter of a century, I have Mexico right up there at the top of my list of favourite countries I’ve been to. Where is the other? Well, I’ll tell you, in a bit. 🤣 I would easily recommend Mexico for the trip of a lifetime. The first time I went was in 1998, and we rented a van and drove down from the US through the desert to Puerto Penasco. After arriving in the dark and drinking too much tequila, we woke next morning and it was beautiful - I nursed my hangover warm flat Coke and huevos rancheros whilst watching pelicans diving for fish, a thing I still love to watch now when I’m there (I did it last week, between hurricanes, but minus the hangover!)
For the adventurous, the first thing you need to do is get out of Cancun, which is the airport you probably arrived at. It’s a shithole, aimed at American underage drinkers. The Mykonos or Ibiza of Central America - but no one assumes the rest of Greece and Spain lack culture or natural attractions just because there’s a party vibe going on in one corner! That would be the opinion of the uneducated. If that describes you, let me enlighten you.
Leaving Cancun to the west, you can first visit Valladolid before coming to Chichen Itza, the best restored Mayan ruined city. It’s amazing, and there are well known cenotes nearby to swim in, Ik-kil being the most famous of many. This is the furthest many get from Cancun on a day trip, so is fairly well known, I won’t describe it further here. Wandering further along this road you pass various other smaller Mayan sites in various states of excavation, before coming to Merida. A fascinating little city few visit, with great nightlife (less frenetic than Cancun) and restaurants, it’s a very good place for stocking up on traditional Mexican crafts such as hammocks, glassware and carvings. It’s not far from Merida to sleepy Celestun, one of Mexico’s many Biospheres, where you can take boat rides through the mangroves and see flocks of flamingos in the lagoons, and go looking for horseshoe crabs, giant iguanas, howler and spider monkeys, raccoons, and coatamundis. From Celestun or Merida, head south along the Campeche coast, taking in more little towns, cenotes, jungle and Mayan sites. Eventually you begin to get to the highlands of Chiapas, and this is a wonderful place (if a little questionable on the rebel activity front!) Jungle ruin Palenque is the standout sight, but Tonina is amazing too - Mayan sites with very few visitors given their historical importance (mainly because they are so difficult to get to.) We rode horses up into the cloud forests near Tonina, through the Spanish moss and orchids, and watched fireflies lighting the sky as we slept in hammocks hung in a cabana on a mountainside in the jungle. The cascading clear blue waterfalls of Agua Azul are worth a visit too. Onwards towards San Cristobal de las Casas, another beautiful and traditional town in the highlands, famous for its culture and traditional textile work.
From here you have a choice - you are halfway to Mexico City, and could continue on to there with all of it’s Aztec history and sites, as well as more recent Mexican culture. Or you can head back towards Cancun, which is the route I know better (having done it 3 times, taking around 3 weeks each time but seeing new things every time I went.) Or, for the very adventurous, you could turn southwest into Guatemala through the endless dense jungle of El Mirador National Park, to see Tikal, the greatest of Mayan cities, onward through Belize, and return to Cancun that way.
I chose to stay in Mexico, so many things still to see there, and went through the northern part of El Mirador NP, spending a night feeling like Lara Croft at Calakmul along the way. We didn’t see a jaguar, but many do here. I wanted to spend more time on the Yucatan coast. Once by the sea, I visited the shimmering turquoise waters of Laguna Bacalar - famous Instagram location now but deserted when I stopped for a swim there. UNESCO World Heritage Site, the Sian Ka’an Biosphere and down to Punta Allen next for a long tailed boat through the lagoons to see manatees and dolphins in the wild, as well as eagle rays, saltwater crocodiles, massive turtles, and endless bird life - everything from frigate birds to eagles to tiny hummingbirds. You can take trips out to the Mesozmerican reef (the second longest barrier reef in the world) to scuba dive, and beyond to see the whale sharks.
Northwards, you begin to come back towards the more touristy places, but they are still worthy of your time! I spent over 2 weeks just on this bit once, with my children who still rank it as one of the best holidays ever. Basing ourselves in Tulum, the first time I went I stayed on the beach in a tent, the second time, in a $10 dollar sand floored cabana I had to provide my own hammock for, the third time we had a bed and our own bathroom but still the sandy floor of a traditional cabana. However, you could stay in a top end yoga retreat cabana like something the elves built in Lothlorien if you wanted to splash the cash. Beautiful bars and restaurants - the best margaritas are here, and one night under the full moon we watched hatching turtles crawling down to the surf. Two Mayan sites are worth your time here - the obvious one of Tulum, still spectacular on its cliff top even with all the day trippers from Cancun, and Coba, deep in the jungle and containing the only pyramid I know of you can still climb to the top of (I’ve done it twice. Still terrifying.) Moving back up towards Cancun you are now into the Riviera Maya tourist zone. You can still find secret little cenotes to cool down at where only the locals go, but there are the big ones too, where you can raft, paddle board, climb, snorkel and scuba through the caves, watching the blind fish below you, and if you go at sunset - the bats as they leave their caverns for their nights hunting.
Into adventure park territory now, Xel-ha is still fabulous, despite the number of tourists. For a one stop experience, you can see mangroves, shallow reef snorkelling, zip wire, tubing along a freshwater river with cliff diving spots along the way, and the restaurants and bars are included. Xplor is where the big zipwires are though, equally as good at night as during the day. Playa del Carmen is a tourist town but less ‘drunk yanks’ than Cancun, and a good base for boat trips, sailing, scuba and snorkelling. Go further north though if you want to snorkel or dive at the Museum of Under Water Art (MUSA,) the first modern sculpture park of its kind, and certainly the biggest. You can see this if you take a boat trip to Isla Mujeres, although sadly these days that is just an extension of the worst tourist traps of downtown Cancun, no longer one of the most beautiful beaches in Mexico.
Even on a single night stop in Cancun, with little time to get out, I still find something wonderful to do - most recently I took a kayak deep into the Nichuptze Lagoon directly behind the zona hotelera.
Or, you could be like some of my colleagues, and say ‘Mexico? It’s shit. Nothing to do except sit on a beach, or go to Coco Bongos.’ 🙄 It’s all about your mindset.
Anyway, back to the OP @soundsintheair - if you are doing it properly, 3 weeks for this trip of a lifetime will not be enough. Best be fair to your colleagues, hand your notice in now so you don’t drop them in it over Christmas, and plan for longer. It’s really not fair to issue your boss a ‘give me the holiday or a leave’ ultimatum. The polite way to have done it would be to have asked properly before booking, or accept that you will have to leave your job gracefully in order to pursue this adventure. I sincerely hope that you don’t class 3 weeks of sitting on the beach in Cancun as the trip of a lifetime! You will be disappointed!
And where is the other destination in my top places for the trip of a lifetime? Well, you’d be brave to go there atm, but Jordan with it’s deserts and reefs, entire ruined cities from Petra to Jerash, Crusader castles and medieval history, Dead Sea, biblical sites from the place where Moses saw the Promised Land to the river where John the Baptist baptised Jesus, its welcoming Bedouin culture, rock climbing, star gazing, dune bashing, camel riding - it comes close to perfection imo as the trip of a lifetime. But maybe not for now.
Costa Rica? Nice enough, but for those who haven’t really travelled and want somewhere safe and popular to go and read about it once in a magazine. Don’t get me wrong, I’ve been, and I’d like to take the family as it will be fun, but don’t sneer at Mexico and suggest Costa Rica instead. Comparing apples with oranges there.