Old Goa (or Velha Goa in Portuguese) is located in Panjim. We can notice a strong Portuguese influence in this town thanks to the various churches.
The most famous in the area is the Basilica of Bom Jesus which is a must visit thanks to its beauty but also to understand the history:
However, this is not the only interesting piece of architecture in Old Goa. The town is apparently full of surprise and good to get some knowledge.
I think it is then worth to stop there for a few hours visiting other churches and chapels such as the church of Francis Xavier.