Huaraz, Peru
Reddit: For me the nature / mountains are clearly the best part of Peru. The cities are not that amazing, though Cusco is quite nice if you don't mind the crowds of tourists. I didn't get to see the jungle side of Peru, so don't know about that.
My favorite experience was the Salkantay trek (5 days, 4 nights) to Macchu Pichu, but in my opinion the trek itself is better than the destination. Santa Cruz trek (4 days, 3 nights) was a close second to Salkantay; the views on Santa Cruz are actually better than at Salkantay, but we had a MUCH better trekking company and group for Salkantay, which made it better overall.
Other places we visited from South to North:
Lake Titicaca: The Bolivian side is better than the Peruvian side, as the Uros islands are very touristic. Isla del Sol is beautiful and definitely worth a visit. You can probably get there from Peru, but we did it from Copacabana, Bolivia.
Cusco: Nice city with lots of tourists. The sacred valley tours are worth the money; very nice places / ruins. The rainbow mountain is also cool, but the red valley next to it is even more amazing, and not that many people go there for some reason.
Arequipa: Overrated in my opinion. "The white city" is like 10 blocks and after that there's not much. The Colca-canyon is a decent hike, but after the praise it gets I was expecting more. There are many MUCH nicer hikes that don't get half the praise.
Huacachina: Nice views from the dunes. Worth a stop since it's in the most common route thru Peru anyway.
Lima: Not a bad place to hang out, but probably not worth it if you have just two weeks or something.
Huaraz: Amazing hiking opportunities / day trips. The city is alright too.
Trujillo: One of the ugliest and least friendly cities I've visited. Avoid if at all possible.
Mancora: Quite nice beach side town for chilling out if you're going to / coming from Ecuador. Far from everything else though, so if you're flying to Cusco / Lima it's too remote.
Must sees.. In my opinion either Cusco with Salkantay or Inca trail, Sacred Valley, Rainbow mountain.. Or Huaraz with the activities there. So pretty standard stuff!