I visited this WHS in June 2019. It was a last minute addition to my already packed itinerary but I'm glad I sacrificed a night in Lima for a night in Arequipa instead. Instead of using the night bus from Cusco, I opted for a comfortable early morning flight of only 1 hour. The airport is very close to city centre and the first thing you'll see in the desert landscape is the 5825m high active Misti volcano.
The main square Plaza de Armas was a bit disappointing as not much goes on there unlike other main squares in Peru. Perhaps being so big doesn't help in such a hot climate as most people who pass through the square, do so using the shaded arcades (Arequipa's marble UNESCO WHS inscription plaque can be found here). The Cathedral too seems to be too huge and out of proportion, in fact it is considered one of Peru's most unusual colonial cathedrals since the Spanish conquest. The highlight near the square is definitely the ornate facade of La Compania church which like most of the historic centre monuments and buildings is made of ashlar (sillar). This white volcanic stone is exceptionally soft, lightweight, weatherproof and emerged as a seismic structural solution in such an earthquake prone city. Several external buttresses can be seen all over the historic centre to help the structures from collapsing. In the Santa Catalina monastery you can still easily spot the damages caused earthquakes.
The second highlight of Arequipa is without doubt the monastery of Santa Catalina which alone justifies Arequipa's inscription. It is practically a closed city within a city, so allow at least a couple of hours to explore it. Most of it has been converted to an 'outdoor' museum while the few remaining nuns are confined to the a small part of the monastery. There are free lockers just next to the entrance which is very convenient. The whole atmosphere is very serene and pleasant with hummingbirds buzzing by from flower to flower in the polychromatic surroundings. The different cloisters and 'streets' are heavily influenced by Spanish architectural styles and after a while you'd think you're somewhere in Andalucia, Spain. The paintings with indigenous elements embellish this unique monastery.
For panoramic views of Arequipa and the Misti volcano, the Yanahuara viewpoint is a favourite spot for sunset among locals and tourists, while a typical dish worth trying is stuffed red peppers with cheese.