There are a few historic buildings, mostly churches in the city center. It may be difficult to spot them as they are squeezed between modern buildings. Church of St. Anthony (Igreja de Santo Antônio) and Church of St. Francisco (Igreja de São Francisco de Assis) are good examples. The oldest part of the city is the Patio de Colégio. It is where São Paulo de Piratininga was founded by the Jesuits Anchieta and Nóbrega. The small building you find there does not look like historic one. The square is surrounded by Manhattan style buildings.
It is worth visiting the Mercado Municipal (Municipal Market) for lunch break. There are over 10 restaurant-bars that serve among others local food on the mezzanine. It is true that the definition of locality in the case of Sao Paulo is difficult. Each cuisine is local in Sao Paulo.
We did not know what's what on the menu. So we discreetly looked at the plates on nearby tables. It was not difficult because tables where set the way they formed one long table. Discretion proved to be indiscreet and after a while a couple sitting next to us offered help. They described what other people were eating. Perhaps we could order any food. A queue of local people waiting for tables was a proof that it was the right place for trying the local cuisine. And it was good.