Peru beyond Machu Picchu: what else is actually worth seeing?

We have 2 weeks in Peru next July and Machu Picchu is obviously happening (doing the Salkantay trek). But that only takes up about 5 days. What do we do with the other 9?

I’ve seen Rainbow Mountain, Colca Canyon, Lake Titicaca, Huacachina, and the Nazca lines all recommended. Problem is they’re all spread out and domestic flights in Peru aren’t cheap. If you had to pick 2 or 3 of those, which ones were actually worth the effort to get to? And which ones were kind of a letdown in person?