It is next door to Aras an Uachtarain, home of the Irish president currently Dr Mary McAleese and her family which you can also visit for free if you are lucky.
A limited amount of tickets are issued each Saturday at the Pheonix Park Visitor Centre. However Farmleigh is open all year round unless it is hosting government functions and its also free If you visit around Christmas time the house is beautifully decorated but a pleasure year round nonetheless with beautiful staterooms, a magnificent galleried Jacobean wood panelled library and Victorian conservatory complete with potted palms.
Outside there are very well maintained formal gardens including a Dutch sunken garden which has three descending terraces to an oval pool with a carrara marble fountain as its centrepiece. There are regular free events for children including storytelling and puppet shows at Christmas. And for adults free ticketed musical events, artisan food markets, gallery exhibitions etc. Or if you fancy letting someone else do the cooking a contemporary restaurant in the Boathouse on the lake.
For more things to see and do in Dublin visit www.irelands-hidden-gems.com/dublin.html