The best way to get to Introdacqua is to take the train to Sulmona (the closest town with a station). From Sulmona take a 15 minute cab ride into Introdacqua. You can also catch a bus from Sulmona (tickets from tobacconist, timetables from the Information Centre, departing from the bus-stop beside the park). It's only a few kms from Sulmona, so you could walk.
If your not brave enough to rent a car (I wasn't) then just use your feet. The town is so small you can cover all the hills in one day at a very steady pace.
What to do? Relax, Enjoy, Breath! That all there really is to do here. Visit the town square, the church, the cemetary, and the tower. Meet the local Italians!
The high part of Introdacqua is old (10th Century) and a mix of ruins and renovated apartments. Check out the square tower. In the lower part of the town is the Palazzo of the Trasmondi Marquises and a lot of quaint 18th century houses with iron balustrades.
Carlo will make you anything you wish, he is kind of like a genie! Beyond great food, seriously