Quick Tips & Getting Around
If you plan to visit Nemrut Dagi, stay in Urfa (aka Sanliurfa). There are several other towns to choose from and some are closer to the mountain itself, but Urfa has the most to offer, with more accommodation and restaurant options and its own sights of interest
A recommended tour from Urfa (which I didn't take) is to Harran. According to the Book of Genesis, Harran was briefly home to Abraham and his family. This ancient area is still covered in distinctive beehive houses made of baked mud. One reason I didn't make time to go is that there isn't much left to see—however, with a good tour guide to explain, it should be worthwhile. Harran and Nemrut Tours in Urfa is excellent if you get the owner as a guide
Don't plan too long for Olympos. It is beautiful but crowded, and hardly a beach paradise. Unless you are with a huge group of friends, it can be kind of boring
Have a good phrasebook, or learn to be comfortable with gestures and lots of patience. Few people speak English in the Southeast. Few people don't speak English in Olympos
I took a chance on using a Footprint guidebook, not wanting to be dependant on Lonely Planet. I'd heard Footprint was excellent for South America, and LP had really let me down in Egypt. But for Turkey, Footprint's not quite there yet. Explanations for getting around are poor to nonexistent, the maps are difficult to read, some of the hotel recommendations are iffy, and the sheer number of spelling errors is very distracting. LP books on Turkey are updated frequently while the last Footprint is from 2001. It's less of an issue in the touristy parts, but I had some trouble in the Southeast.
The older editions of LP were written by Turkey authority Tom Brosnahon. Check out Tom's Turkey Travel Planner for great starting info on the whole country.
Getting Around
The bus. That's it. Get ready for sore asses. Extra sore for me, as I came from Syria. It was almost 4 hours from Aleppo to Antakya, at which point I transferred to a 9-hour bus to Sanliurfa. From Urfa it was about 3 hours by bus to Antep. After a stop in Cappadocia (7 hours away from Antep), I rode another 10 hours down to a mountain area near Olympus. Which then requires a transfer to a smaller bus that actually goes down toward the beach. The return is then...13 hours to Istanbul
Urfa and Antep are walkable small cities. From Urfa's bus station I took a taxi in to town (and got ripped off), but from Antep I took a local bus to town instead. Once in town, you can basically walk everywhere. Walking south toward the lake in Urfa is especially pleasant, passing numerous mosques and the souk along the way.
Olympos' main "street" is basically all hotels. Where I stayed, it was about an 7-minute walk to the start of the ruins, then another 10 minutes to the water. Some hotels are farther and provide shuttle service.