We spent 2 wonderful weeks in Peru this year with 15-month old ds, and despite being pfb, had a wonderful time.
We did it independently, which is what I think made all the difference - you need to be able to just spend a lazy day somewhere if he's tired and not try and force him to fit in to a group's schedule.
It was the first time we went "proper" traveling with him, so was pleasantly surprised to see how much he enjoyed it. You need to keep in mind though that, should your dc feel bad / grumpy etc, you'd need to abandon plans to travel around and stay put for a bit. If you'd be able to have fun anywhere, then I'd highly recommend it. If you're not flexible, I'm not sure if it's not too risky.
South America (well, Peru, but apparently others are known for it too) is very child-friendly (the people). Everywhere we went - from Machu Picchu to the Amazon, people went out of their way to entertain him. If you do go to Peru, which I loved, keep an eye on altitudes. For example, whilst we would have loved going to Lake Titicaca pre-ds, it's too risky (well, in my opinion) with a young child. He loved the Amazon (but again, be careful where you pick - we went to a low-risk malaria zone), and he loved Machu Picchu, but we spent 3 days acclimatising at lower level (in our case Ollantaytambo) on arrival in Peru before doing the trip.
Have a look at the Lonely Planet Kids to go forums had some great advice from nutcases more adventurous parents.