County Kerry: See
County Museum in Tralee is a good introduction to the area.
Killarney is the tourist capital of Kerry. It's got the lot: a well-repaired castle by the lake, an atmospherically shabby abbey, grand gardens and a museum of country life, Ogham stones inscribed with runes, and Ireland's highest mountains rearing up to the west.
Prehistoric remains are common in the less-populated areas. The main concentration is west of Dingle.
Early and medieval Christian sites are dotted about, with a good example at Ardfert near Tralee. The most remarkable, thanks to its remote setting, is on Skellig Michael.
Castles: the best preserved is Listowel. Many others are just scenic stumps, such as Carrigafoyle perched at the water's edge on the Shannon estuary. Ballycarbery near Caherciveen could be mistaken for prize topiary, while the Disneyesque schloss in Caherciveen is the old police barracks.
Bird life: the rugged coasts plus Killarney National Park have the most. See Kerrybirding for specific locations and recent sightings.