We are heading on an 11-day tour of Ireland in June. We are arriving one day early and would love to see the Gardens of Powerscourt and Glendlough. The highly recommended Mary Gibbon's Tour is booked solid. Are there other, similar day trips to these locations?
You can also ask at the Tourist Information booth at the airport when you arrive. They have information about all sorts of tours.
Check out www.dublinbus.ie This is a good site. Start location is in downtown Dubs on O'Connell Street at the same location where the Hop-on-Hop off tours start at the main bus station.
I've taken the bus Eiren tour from Dublin to Newgrange and Hill of Tara. We were pleased with them. The price was very reasonable for a full day of touring. We picked up tickets at the bus station the day before. They also run a bus South to Glendalough. While the bus driver may identify points of interest, it isn't a guided tour. These are popular spots. When you arrive there are visitor centers and tours available. They allow enough time to take a tour and wander around before the bus leaves for the next destination.