Driving
Renting a car is by far the best way to discover Ireland (outside of the cities) but it can be a more expensive option, particularly for younger visitors under the age of 21 years, as insurance is quite expensive.
The following web-site will aid in planning a route and give a rough idea of journey time. But take those times with a "pinch of salt"; they're a bit optimistic and don't take roadworks, traffic delays and diversions, sheep on the road (yes, really!) etc, into consideration. Recommend you add on a further 15% to journey times to reach realistic figure.
http://www2.aaireland.ie/routes_beta/
Distances and Minimum Drive Times Between Dublin and Popular Destinations (from aaireland.ie):
Dublin-Cork: 255km; 3hrs, 4min
Dublin-Dingle: 346km; 4hrs, 48min
Dublin-Galway: 218km; 2hrs, 43min
Dublin-Kilkenny: 123km; 1hr, 42min
Dublin-Killarney: 302km; 3hrs, 54min
Dublin-Sligo: 208km; 2hrs, 52min
Dublin-Westport: 252km: 3hrs, 30min
When you are travelling around Ireland, it is important to remember that many of the more spectacular areas are very sparsely populated and the roads in these areas are usually narrow and traffic can be quite slow moving.
Please don't underestimate how long it will take to drive from "A" to "B", particularly through rural areas, where the average speed is around 30-35 miles per hour, 50-60km per hour. Roads outside the main cities are usually single lane (one lane each direction), and in some areas, only the width of a single car: be prepared to reverse into a drive-way or passing area.
Photos of typical rural roads around Ireland: Beara Peninsula:
The Burren, co. Clare:
Slea Head, Dingle Peninsula:
The Mmjor inter-city roads are a lot better, and are increasingly being replaced by full motorway (expressway); most of these projects are now complete.
Routes between smaller cities and towns are usually fast moving, but are often a single lane in each direction.
Trains
http://www.irishrail.ie/your_journey/...
Special summer offers from Irish Rail can be found at http://www.irishrail.ie/news_centre/n...Due to the low population density in Ireland, the rail network is less extensive and the frequency of service is less than in most other European countries. However travelling by train is generally a comfortable way to see Ireland. For journeys between Dublin and Cork and Dublin and Tralee and points in betwen the train is generally much faster than driving or taking the bus. The Dublin-Rosslare line is very slow and the bus is generally faster. However, the train to Rosslare wins hands down if the purpose is to gaze out of the window. Travelling South, after having left the Dublin suburbs, the line clings to the coast as far as Wicklow. Turning inland, it runs through verdant pastures through Arklow, Gorey and Enniscorthy. Beyond Enniscorthy, the line clings to the side of the River Slaney all the way to Wexford. That's three hours of views that you cannot gain by any other means of transport! For other routes the train is generally about as fast a driving and a bit faster than the bus.
Bookings
You can usually take advantage of cheaper fares if you book online in advance through www.irishrail.ie
If you haven't got a seat reservation and are travelling at weekends or over holiday periods, be sure to arrive at the station at least 30 minutes before departure otherwise, you may have to stand for your journey!
On the website "standard" means that you have a seat number allocated and "ticket only' means just that. Not all trains can be reserved and not all seats can be reserved on any train. Seat reservations are only possible on the web, not at rail stations. On the Dublin-Belfast "Enterprise" service there is "1st plus" and some Dublin-Cork trains have "CityGold" both of which offer a roomier coach with 1+2 seating instead of the normal 2+2, complimentary coffee, etc. On other routes there's really very little difference in comfort between First (Premier) and Standard class.
Unlike Amtrak in the USA there is no "check-in" process. You simply find your train, and your seat if you have reserved one. You can turn up 1 minute before and still board, though this is not recommended for the faint hearted !
If you have made a reservation, your name will be displayed on a little electronic display above your seat on newer trains (e.g. all trains on the Cork-Dublin route)
The Cork-Dublin Train:
Standard Intercity Trains to all other destinations (except Belfast). These are being rolled out across all routes in the Republic, and already serve most desinations on the network.
Buses
http://www.buseireann.ie/bubble.php? i...
Information on Bus Eireann tourist fares can be found at http://www.buseireann.ie/inner.php?id...The bus network is much more extensive than the rail network and buses are often considerably cheaper than trains. On the main inter city routes services are frequent but off the beaten track there may only be a one trip a day - or per week - so advance planning is essential. Services are operated by a number of different bus companies, the largest of which is Bus Eireann. Details of other operators' services are harder to come by - try the page on Wikipedia which lists companies offering services to & from from Dublin. A number of Bus Eireann direct services are operated from a number of Irish Airports to different parts of the country: see
http://www.buseireann.ie/inner.php?id...
Ferries
When planning a trip around Ireland, keep in mind that taking ferries across rivers can help cut down on travel time, if you time it right. For information about ferries across the river Shannon, see www.shannonferries.com. For general driving directions for anywhere within Ireland, see the useful AA Ireland site.
**Note: The original information for this paragraph came from the following forum thread: http://www.tripadvisor.com/ShowTopic-...