Streets of San Blas
There was a local festival one of the days we were there, which started with letting off fireworks in the middle of the night, and continued all through the next day and night with brass bands, more fireworks, and some serious day drinking. The guy with the pyrotechnics had clearly been on the piss for several hours when we went to investigate at around ten in the morning. Every so often, he would produce a few rockets and launch them from the middle of the square. You couldn't see anything, but the explosions were loud enough to set off car alarms. This happened several times an hour, from around four o'clock that morning until he either ran out of explosives or died of alcohol poisoning around midnight.
The city is full of museums, of varying quality. We went to the Qoricancha Site Museum because it was included in the boleto turistico, and because there's a nice little park behind it that you can only get to by going through the museum (or by dodging security guards). This was possibly the worst museum I've ever been to: a dank underground bunker with a strange collection of artefacts that looked to have been salvaged from another museum's bins, and with explanatory text written by a class of bored 11-year olds.
The Museo del Convento de Santo Domingo Qoricancha is completely different, and well worth seeing. This was once the most important Inca religious site, with amazing stonework and walls literally covered in gold. The conquistadors pillaged all the gold then tore most of it down, and built a Dominican church on the foundations, which has magnificently weird paintings inside. All the angels are portrayed as Andean children (one wearing a very cute Elmo sweatshirt), and above the choir stalls there are superbly detailed pictures of saints and important Dominicans all looking as though they're about to smite some serious evil. Or are possibly auditioning to be part of a new Christian-themed fantasy trading card game. They don't allow photography or sell postcards, though.
Inside and outside the Qoricancha museum
The Centro de Textiles Traditionales de Cusco, just down the Avenida del Sol from the Qoricancha gardens, is definitely worth a visit. There's a small museum gallery that does a very good job of explaining local textile traditions, and a lovely shop that often has women weaving or sewing. I picked up a lovely scarf of undyed alpaca that had been hand woven by a woman called Felicitas Huaman Quillahuaman in Chinchero.
The Museo Histórico Regional de Cusco is in the house of Garcilaso de Vega, the son of an Inca princess and a conquistador. He lived in Spain for most of his life, and wrote important chronicles of Inca history and culture. Sadly, the museum suffers from the tendency to cram as much in as possible without much explanation, but the building itself is well worth the visit. There is an interesting room focussing on local cuisine, with a Cusco-school religious painting showing guinea pig being served at the Last Supper.
Cusco is definitely a tourist town. There are lots of people on the street trying to persuade you to eat in their restaurant, and women in traditional clothing demanding money for photos. Several of them had beautifully well-groomed llamas with them.
Food notes: we had surprisingly good Indian meals at Cafe Carvalho and Maikhana; tasty high-end chifa at Kion; and disappointing Japanese at Kintaro. La Bondiet makes great empanadas, and Papacho's was good, if not exactly cheap.