Mdina, the former capital of Malta, is a very nice city. It already looks interesting if you travel towards Mdina as it's ringed by the city wall. Mdina was build by the Romans, was fortified later by the Arabs and names "el-Medina" (= city) then. It had been the capital of Malta up to the 16th century. Today it's the "Silent City", with only a few hundreds of inhabitants, lots of narrow streets and almost no traffic.
When visiting Mdina, I also recommend to visit the neighboor town
Rabat, it has catacombs and also a nice church!