The nearest airport is Cork Airport (ORK)
Cork Airport serves the following airports and destinations
Amsterdam Schiphol, Paris Charles De Gaulle and London’s Heathrow receive many international flights from the US and abroad, however the main airlines may not serve connections to Cork (see Cork service below). We can recommend flying into London (Gatwick, Stansted or Heathrow) and then taking a budget flight directly to Cork.
Consider booking the leg to Cork with a low-cost transfer (RyanAir, Aer Lingus) - www.google.com/flights can help with this, otherwise check with each airline directly. Norwegian Airlines has low-cost direct flights from Boston to Cork and Icelandair often has good fares as well.
More Airport Options
Shannon Airport (SNN) is 1h15 trip by car to to Blackwater Castle.
Renting a Car
Having a car can make Ireland much more accessible. Please keep in mind that manual gearboxes are standard and cars are right-hand drive. Irish roads are also exceptionally narrow when compared to American roads. We recommend reserving an automatic car to make the experience safer and more enjoyable.
We suggest you rent a car directly at Cork or Dublin airport with one of the many options; Sixt, Europcar, Hertz, etc. We have hired cars with Budget at Cork airport many times and can recommend them from personal experience.
* If you are 70 or older, please ask explicitly about a maximum age policy, as many car rental companies have restrictions on this. *
It is a 50 minute drive from Cork Airport to Blackwater Castle in Castletownroche.