Cusco is a unique blend of a colonial city with the traditions of the Inkas. The colonial buildings often are set on top of Inka foundations and the city has a unique mountain feel to it. Personally, I enjoyed the San Blas Barrio the most which is tucked on a hillside to the North East of the historic city center.

Cusco is also a pretty touristy place as it serves as hub for the area. You will find plenty of Western tourist amenities. For instance, Cusco was the only place along my trip I managed to take a Yoga class.

For a Peruvian city Cusco felt comparatively dirty. I found both the central districts of Lima and Arequipa better upkept. In addition, the original Inka/colonial town layout is very narrow and illsuited for the amount of traffic the city nowadays has. This, though, is a problem Cusco shares with Arequipa and Lima. More pedestrian precincts would be a nice improvement.

Getting There

Cusco is well connected by both busses and planes to all parts of Peru and some parts of the world. Seeing the distances involved I would counsel to making use of the airport. From the airport you can either take a cab or a collectivo. The collectivo run directly in front of the exit. If you are a train aficionado there is also a train connection to Puno. 

Altitude Sickness

Cusco may very well be your first stop on your trip above 3000m. As such altitude sickness may be a thing. In my case, I felt minor headaches from the minute I exited the airport terminal. Wandering around the city on my first day I was quickly out of breath.

 I can only strongly recommend to take it easy and take adequate pauses. If possible, come in via bus to help with the acclimatization or continue quickly to the Sacred Valley and Aguas Calientes/Machu Picchu as these are significantly lower.

While You Are There 

From Cusco you can travel on to Machu Picchu and the Manu National Park. For Manu please be advised that no tour from Cusco lasting only three days will take you to the core zone. The core zone tours last longer and cost significantly more. For Machu Picchu you need reservations for both the site as well as the trains. In off season (Oct to May) this may well be possible at short notice (within a week). If you don't mind spending a bit extra, using a travel agency in Cusco to do all the bookings for you may be worthwhile.

Cusco was also the nexus of the Qhapaq Nan. By venturing a bit further North you can find a remaining part of the road system. Start at the Templo de la Luna and Chukimarka and follow the trail direction Yuncaypata. You will see a big sign with a map and an explanation at the beginning of the trail. This can be well combined with a visit to Sacsayhuamán which is fairly close to the start of the trail.

The Sacred Valley holds many great sites. The terraces at Pisac, the fortifications at Ollantaytambo or the salt mines of Maras are unique and well worth exploring. To me this would warrant at least a serial inscription as cultural landscape, if not several individual sites. In Pisac save yourself the cab and hike up and down. On your way up try to stick to the right hand side and pass through the amazing terraces. On your way down follow the steep mountain ridge.

Finally, you can move on to both Arequipa (bus, plane), Lima (bus, plane) and Puno (bus) for Lake Titicaca. When transferring to Puno I would recommend the tourist busses with multiple stops along the way. The Church of Andahuaylillas is a spectacular example of Barroco Andino and I feel that this could be another inscription. Another stop is Raqchi, a site of the Qhapaq Nan which runs right through it. Upon entering the site head to the site map and you will see a clear demarcation of where the Qhapaq Nan runs.

Notes

I referred to Cuzco as Cusco as it's the current town name. I am not sure why Nazca/Nasca uses the new town name and Cuzco/Cusco the old one.