It is so much fun and so interesting to just walk around gaping at everything.
The Incas were excellent architects and engineers. The stone walls were constructed very carefully with each stone carved to fit tightly so no mortar was needed. It's not too clear exactly what tools they used for the carving. The building walls all sloped inward a bit to help preserve them over time.
You can see some workers (of several species here) doing site maintenance.
Click here for some pictures