The Qhapaq Ñan
This is an overview map of the Qhapaq Ñan, the Inca Highway. (Press here to learn more about the Qhapaq Ñan instead of just maps). It was among the most impressive infrastructure feats in the 16th-century world. The conquistadors lavished praise upon it.
The Qhapaq Ñan spanned some 40,000kms (24,000mi). It is not clear if all 40,000kms were paved, but it was smooth, either with a concrete-like top or stones. In places with heavy rainfall, it had drainage and was built at a slant. In places with heavy snowfall, such as the mountains, walls were built along it to shelter it from blowing snow. In the desert, poles were constructed alongside it to increase visibility in the sandy conditions.
It was built for humans, and only humans because there were no horses or pack animals. It would ascend and descend mountains vertically with little regard for switchbacks. The only traffic permitted was authorized by the state. On the heavily trafficked areas, elaborate bridges made of reeds were built. On the side roads or those that were less traveled, zip-lines, or rafts were utilized to cross rivers and deep ravines.
Also, view this interactive map from World Heritage Organization.