I stayed in Killarney for two nights, and I went cycling one day. I started from the town at noon and followed the route given by the owner of the rental shop. I rode about 30 kilometers. Including the time to stop and visit various attractions, I was able to return to the town at about 6 o'clock in the evening.
Cycling is a little tiring but very fun. Ireland is originally sparsely populated, and it seems that this mountain forest is yours.
Avoid going in winter, it will be scary in the forest when it gets dark early~