Gotcha. We had 4-nights there last year. Purpletraveller's post sums it up very well. We did all those things. We also had a trip to Mdina (about 30-40 min bus-ride) because the wife is a GOT fan (and it was a great wee medieval walled town!) and a day-trip (similar bus-time) to Marsaxlokk where we saw the traditional Luzzo boats and had a ride in one to the grotto. However if you're just there for the day.. would look at Purpletraveller's recommendations. We enjoyed Fort St Elmo.. but even just wandering round Valetta admiring the old buildings, city walls etc was great.