The fast and furious rundown: From Puerto Escondido, it's easy to get an overnight bus into Oaxaca City, and I arrived in the first week of a huge, annual indigenous culture celebration called Guelaguetza. (Lucky coincidence for me, worth planning a trip around for you!) There were Aztec dancing demonstrations, mezcal tastings, prehispanic food offerings and more bazaars than usual, in a city that's known for bazaars.
There were parades, with marching bands and folk dancers and giant puppets. You could join the parade, walking alongside it for hours, much like a Second Line in New Orleans.
Oaxaca is a colonial city, so it has a bit of a European vibe (ornate cathedrals, universities), and it's the capital of the state of Oaxaca, so it's also quite urban (fantastic restaurants, street art, museums - including the stellar contemporary art museum MACO - and galleries and boutiques). Because of it's strong indigenous culture, it's a political city. There are constantly people demonstrating. When I was there, there were multiple protests -- an artist in a tent in front of Santo Domingo church on a hunger strike against deforestation and hundreds of teachers who had been living in El Zocalo for months, protesting low wages.
If you want to buy gorgeous handcrafted textiles, Oaxaca is the place. If you want to eat chocolate for every meal (hot chocolate for breakfast, mole for lunch and dinner), Oaxaca is definitely the place. And the food on the street is as amazing as the food at the trendy restaurants, so it's really a matter of atmosphere and how much you want to spend. (I only went to one "high-dollar" restaurant, which is priced "moderately," $15-20, by US standards. Casa Oaxaca, in the upscale, arty neighborhood of Reforma, is bright and uncluttered, in terms of both decor and food.)
Convenient day-trips from Oaxaca include Hierve el Agua, a calcified waterfall about two hours from the city, with two spring-fed, nature-carved "infinity" pools. The pools are open for swimming (the springs are hot, the pools are not), and there's hiking and abundant mountain views.
Milta, a charming little wander-able town with an important archeological site and more bazaars, is the halfway point. Usually hotels can set up a tour for you that includes Hierve, Milta and mezcal factories, but I just took a collectivo and skipped the mezcal factories. (If you do it this way, you might get to ride in the back of an open-air truck. This is great fun, because the views are stunning.)
From Oaxaca, I flew back to Acapulco. NOTE: IF YOU DON'T SHOW UP AT LEAST AN HOUR AHEAD OF TIME, AEROMEXICO WILL GIVE AWAY YOUR SEAT. And that will not be fun. You will end up spending a night in Mexico City at your own expense and getting up for a 5 a.m. flight, so you won't even get to enjoy your cushy hotel.
Before this mishap (I showed up 45 minutes ahead of time), I'd booked an Acapulco beach hotel and planned to spend my day lounging, before catching an evening flight back to Arkansas. Because I actually arrived in Acapulco in the early morning, I had no need for a hotel, but I didn't want to waste the entire day at the airport. I was also low on cash, had maybe 50 pesos -- way too little to take a cab anywhere, and I didn't want to change any money, since I was on the way out.
One of of my favorite things about traveling is finding yourself in unusual situations and having to make it up as you go -- seeing how you react when you can't communicate well and spent hours on a bus, only to end up in the wrong town, or you find yourself broke in the middle of nowhere, with no ATMs, or your hotel room door doesn't lock and the "manager" is nowhere to be found. I like the challenge of having to be unexpectedly resourceful.
I wanted to go to the beach. Mexico beaches are public, but beachfront property is private, so I knew I had to access the beach through a hotel. And beachfront hotels don't let you near the beach without reservations. I schelped my bags to a bus-stop and took a local bus to a fancy hotel complex. Then I took a cab into the complex, because I was pretty sure arriving on foot wouldn't be very convincing when I told the guards I was on my way to make reservations. The guards didn't speak English, and I pretended not to understand their Spanish at all. They didn't want to let me in, but I was persistent and really played up the miscommunication thing, and ultimately they let me go.
Once I hit the beach, I was home free...I picnicked on airport food purchased with vouchers (my Aeromexico consolation prize, since my seat was given away) and swam, always with an eye on my bags, then cleaned up after in the hotel's poolside bathroom and bartered a ride with a local cabbie back to the airport. (Told him I had 35 pesos left, and he said fine. He'd just been hanging out chatting, anyhow.) And that was that.
Hasta la vista, Mexico!