What type of trip/experiences are you interested in, and at what level of pricing? There are so many things to do/see in Peru. We did 8 weeks there in 2017 as our first big retirement trip, and thought we didn't devote quite enough time. We found most of the country very amenable to travel by scheduled bus lines...
Here is DW's blog archive if you are interested in a lot of photos by destination within the country.
https://www.lisajtravels.com/archive (a bit over 30 posts, no ads/revenue)
As noted by several people, the Amazon Basin is really neat. We enjoyed the upper reaches of the tributaries in the Manu Biosphere Reserve more than the "big river" near Iquitos. We did about a week on small boat and unelectrified lodges to hike and photograph wildlife. We loved it--but definitely would qualify as roughing it in most folks' minds.
Highly recommend Salkantay trek to Machu Picchu if you are up for high altitude, multi-day hiking (We did it "lodge to lodge," instead of Inca Trail; opposite of roughing it.) As an alternative or an addition to Machu Picchu, consider Sacsayhuamán, in the heart of Cusco; due to overcrowding at the former, we may have preferred the latter. Although the climb up (and view from) Huayna Picchu was amazing.
Multi-colored (seven-color) mountain outside of Cusco gives you a neat, short hike to almost 17,000 feet with great views/topography.
Explore Colcha Canyon via a multi-day hike, along with the high plains getting there (Andean Condors are easy to see on this side-trip).
Museums, museums, Cathedrals, etc.....
Lake Titicaca was a worthy side trip. One of our favorite cities was Arequipa, where we stayed for several days (it was our hopping off point for Colca Canyon).
if you are into "blow that dough" food experiences, make your reservations early for Central and Maido (our favorite of the two) in the Miraflores neighborhood of Lima. No matter what though, enjoy the food at all price points throughout the country.
Oh--we also spent about a month in Northern Chile and Argentina in early 2020, and are planning another 2 months in those countries later this year. For us, no way would we try to combine Chile and Peru in a short three-week trip. But, YMMV.