1. Guinness Store House
This is expensive (adult tickets are €;13.50, or almost $19), but no trip to Dublin is complete without a visit. Simply every tourist in Dublin seems to come here at least once. The Guinness Storehouse is a hugely impressive building: the core of the building is in the shape of a giant pint glass, and consists of seven floors. Along each floor, you get to see the process of how Guinness is made. The top floor, which has the Gravity Bar, is the most fun: with a complimentary pint of Guinness, you can get the most spectacular view of Dublin, which is worth the admission price alone.
2. Kilmainham Gaol
This museum is a must for history buffs. Kilmainham Gaol tells the story of Irish history: a lot of Irish nationalist leaders were imprisoned there over the years, and most famously, the leaders of the 1916 Easter Rising were executed there. Although this is located about a 15 minute bus ride from the city center, you can make a day of it by also visiting the nearby Irish Museum of Modern Art.
3. Trinity College Dublin
Of course, this is best known for the Book of Kells, but it's worth going here to look in the Long Room, the room in which the book is held, which is just as impressive. (This was the inspiration for a room called the Jedi Archives, in a scene from the movie, "Star Wars Episode II: Attack of the Clones.") It is also well worth taking one of the guided tours around the College: every building seems to have an interesting story behind its - the college was founded it by Queen Elizabeth I in 1592 - and the tour guides always seem to add a little dramatic flair to their tours. The campus is especially amazing during the summer: a popular activity among its students is to sit out outside the Pavilion Bar (known as "The Pav"), while watching a game of cricket.
4. Phoenix Park
This park is the largest urban enclosed park in Europe, and is more than twice the size of New York's Central Park. As with all outdoor pursuits in Ireland, the rain can be a real downer for a day here. But on a good day, this park is a real treat. It's the location of the residence for the President of Ireland, ras an Uachtaráin, as well as Dublin's zoo.
5. National Gallery of Ireland
Although Dublin now ranks as one of the most expensive cities in Europe, at least entrance to this museum (for the permanent exhibition) is free. The museum collection includes some 2,500 paintings and around 10,000 other works in various forms. Major Irish work includes that of Jack B. Yeats (the brother of William Butler) and of Louis le Brocquy, Ireland's greatest living artist
This is the home of the Irish parliament, and is a truly magnificent building, full of history. Although admission is free, tours for this have to be arranged in advance: according to this Leinster House website, visitors from outside Ireland must contact their embassies or honorary consular representative, who can then contact the events desk of Leinster House.
7. Croke Park
This is the headquarters of the main sporting body in Ireland, the Gaelic Athletic Association (GAA), who are in charge of the two ancient Irish sports, hurling and Gaelic football. As well as being the spiritual home of Irish cultural nationalism , it is also the fourth largest sports stadium in Europe - a remarkable achievement for amateur sports. Croke Park can be something of a gem for tourists in Dublin, for the very simple reason that it doesn't seem to be heavily promoted by the GAA with tourists - so if you can get to see a game, the chances are that you will be one of the few tourists there. Tickets for games toward the end of season (around August) can be hard to come by, but there are usually plenty of tickets for the games at the start of the season, around May. It is also well worth coming here to visit the GAA museum and for a tour of the stadium.
8. St. Patrick's Cathedral
Ireland's largest church, and, given its close proximity to Dublin's City Center, a visit here is an essential part of any Dublin tourist itinerary, no matter how short their stay. Unsurprisingly for a church that was founded in the 12th century, there is plenty of history here - Jonathan Swift, the author of "Gulliver's Travels", who was the dean of the Cathedral from 1713-45, is buried here. St. Patrick's Cathedral also hosts choral concerts regularly, which are worth keeping an eye open for. If you do get tickets for a concert here, it is strongly advisable to bring a cushion, as sitting on the hard wooden benches for over two hours can be a fairly numbing experience otherwise.