A fortress on top of a hill (or a mountain, depending on the perspective), narrow streets, authentic architecture, bougainvillea flowers on the walls, views over much of the island, a few restaurants, and a great ice cream parlor (Fior di Latte), with an outlet also by the city gate.
Mdina was a great experience due to its atmosphere, further enhanced by the fact that our living room overlooks this fortress, making it visible to me day and night.
Rabat, which means suburb, surrounds Mdina and is similarly good for wandering around its downtown area.
I’m in a bit of trouble now because I usually explore cities without prior research, so I don’t have the tools for a partial and beautiful introduction. The tactic is always to start exploring, wandering aimlessly, and at a certain point, when I’ve experienced enough, sit under a tree (yes, unfortunately, this won’t work here… :-)) and read what else is worth seeing?
So what?
Maybe the catacombs, but don’t expect them to be spacious or continuous, the prison museum, although I haven’t been there yet. Museums, churches, and other cultural sites are plentiful in these two small towns.
And since I can’t (and don’t aim to) give a detailed introduction, I would mainly advise you to go from Mdina’s entrance with the described strategy, with a Fior di Latte ice cream, and let chance shape the rest. And if there is a bench under a tree (well, actually there are a few wooded parts on the Mdina-Rabat border), then browse through this blog, because it seems they have the tools for a good introduction.