A new attraction opened in 2000 is the Observation Tower at Smithfield, originally part of the Jameson Whiskey complex. You can apparently see all over Dublin city from here. It may be found near Heuston Station, on the north quays. Many westbound buses pass it, including the no. 70. The Luas stop Smithfield is only minutes away.
A most worthwhile journey by train or bus is to Malahide Castle, former (?) home of the Talbot family. Almost all northbound commuter trains from Dublin's Connolly Station stop at Malahide; it is a pleasant 30 minute journey through Dublin's suburbs and farm land (from where much of Ireland's vegetables are grown). It is also possible to take a DART at peak times. The castle is about a twenty minute walk from the station in Malahide village (which in itself is quite quaint and worth a look). The castle features some many medieval rooms and a beautiful dining room with minstrels' balcony. After your visit to the castle, its worth visiting the C. J. Fry railway collection beside the castle which features Ireland's largest model railway collection, based on Irish subjects and rolling stock in 'O' gauge. If you have time, continue northwards on the train to Drogheda [the 'g' is almost silent in its pronunciation with emphasis on 'Dro-'] since it is a beautiful journey over the sea estuaries north of Malahide and at Rush. The parish church in Drogheda holds the head and remains of Blessed Oliver Plunkett and the town is built on the River Boyne, over which is one of Ireland's earliest and most spectacular railway bridges. The Battle of the Boyne took place some miles to the west [near Slane], and was the famous victory of William of Orange ('King Billy') over the Jacobites in 1590. This battle is held dearly in the hearts of the protestants of the north of Ireland as a landmark victory over the catholics, and, in many respects, is the crux of the recent troubles (although British rule over Ireland extends many centuries before this). Despite this, it is not a place of pilgrimage for Unionists, least of all because it is new in the Republic.
Another northside attraction (and very much hidden) is the superb late-Georgian Casino at Marino, about 2 miles from the city centre. This building is often regarded as one of the finest types in Europe, let alone Ireland. It is the only surviving part of what was a large house and garden built for the Earl of Charlemont and it dates from 1758. From a distance it looks like a small folly consisting of one room, but, in fact, it has three floors and fifteen rooms. The interior is full of fantastic detail, plasterwork fireplaces, stucco and the like. It's just off the Malahide Road; take buses 27, 27B, 32A, 42, 42B, 43, 102, 104, 230 from the centre of town (Eden Quay) and ask the driver to let you off.
Train, bus and tram in Dublin 2