Caher Gael is a large neolithic ring fort in a gorgeous setting. The fort has been extensively restored, which may offend the purists, but it is still very impressive. The upside of the restoration is being able to see what the fort looked liked in all it's glory.
At the time of writing this, there is no fee for entry.
Cahergall Stonefort is found off the Ring of Kerry next to Cahersiveen. It’s from Iron Age (500 BC to 400 AD) or the Early Historic period (400 to 1200 AD). It has steps and terraces in the inner face of the wall and with it’s massive walls on which you can walk it was impressing. Also, you have a fantastic view on the Ballycarberry castle ruins and the coast. There’s a parking from which a footpath leads up to the fort. Admission free.