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!
Carlo will make you anything you wish, he is kind of like a genie! Beyond great food, seriously