Kilfenora Cathedral is well wort a visit on any Ireland tours for its high crosses. Especially the twelfth century Doorty Cross which shows 3 bishops and what is probably Christs entrance into Jerusalem. It has beautiful Celtic patterning.
Just East from Kilfenora is the well preserved Leamaneh Castle. This is a fifteenth century O'Brien stronghold worth visiting on any tours of Ireland. It is an impressive four storey building.
The Portal Tombs and Wedge Tombs of the Burren are all within easy striking distance from Kilfenora.
Whilst the Burren is a must see attraction the castle and the crosses are real hidden gems.