When I visited there, the first thing that occurred to my mind was how narrow the streets were.
And because the streets are narrow, the cars are restricted. Pedestrians definitely have more mobility here, while the cars only have a subset of roads that they can use, because the other roads are too small for them to pass.
There were several museums in Mdina, such as the Natural History Museum, but I didn't visit any. Additionally, there are a few churches and cathedrals worth noting, but again, I didn't visit any, as I enjoyed walking the narrow streets more than visiting a church. Besides, I've already visited several churches in Malta by this time.
The thing I liked the most was the piazzas. There are several, not really large, but just a wide space in between the buildings, where several of the narrow streets meet. Some are lined with tables from the cafes. It was a cool experience, being in a walled city. This is a place that I totally recommend for those who visit Malta.