Though for quite a long time lots of ancient buildings were abandoned and brought down by new enterprises, cariocas are usually interested in our own architecture. And one of the best places to see this iconic heritage is downtown, just a few blocks from the port, up hill, in Morro da Conceição.
Besides the old houses and the little old fashioned business, Morro da Coinceição is know for being the residence area of lots of artists that during events open theirs doors for visitation. There a few nice restaurants around it too. Try the marvellous Oswaldo Aranha Fillet at Gracioso or the Feijoada at Imaculada.
Weekends are ok to visit it, but if your plans are having a bite during your stay, try a business day.