Hi again, Simone. :)
Killarney is an excellent choice of destination, as its the gateway to the beautiful
Killarney National Park. Some great walks can be made, or you can take a pony trap or hop-on/hop-off bus to see the major sights.
Killarney is also the starting point of the scenic
Ring of Kerry drive. You can either rent a car and explore it on your own time, or take a guided bus tour. There are plenty of options to choose from, head to the local tourist office for detailed information. This little video might provide you with some inspiration as well.
I hope these suggestions are helpful to you. Other community members might have some great tips and ideas to share with you as well!
Met vriendelijke groeten,
Joris