When I visited Venice during the season of Venice Carnival, I took two tours from this company, Passeggiate Italiane. The one was one day tour in Padova from Venice. A tour guide, who spoke Japanese fluently, took us to famous places, such as the Scrovegni Chapel and Saint Anthony's Basilica. The guide has quite excellent knowledge of Italian art. On top of that, her explanation is quite understandable even for us with no background of Christianity. Because of her nice explanation, we really enjoyed the wall painting of the Scrovegni Chapel, which is one of the supreme masterpieces of Giotto, an architect in Italian Renaissance. We also visited Pedrocchi Café, which is amazingly beautiful caffe shop founded in 19th century.
The other one was a guided tour for Venice. We visited some famous architectures, like Saint Mark's Basilica, with historical explanation of Venice. We couldn't have understood the real meaning of amazing Basilica's interior if we had looked around Venice by ourselves. In addition, the local restaurant, where she recommend us, was quite good. I think it's very difficult for foreigners to find out this kind of venetian restaurant, where local people visited so often. We tasted molto buono venetian dishes.
If you'd like to enjoy genuine Italian art and culture, definitely the tours offered by Passeggiate Italiane are the recommendable ones.