Dublin has no metro. It has two tram lines, a coastal commuter railway and an extensive bus network, and for a visitor the summary is short: walk, and use the trams and the DART when the distance is genuinely long.
Walking distances
Trinity College to St Patrick’s Cathedral, 15 minutes. Trinity to the Guinness Storehouse, 25. Temple Bar to Kilmainham, 40. The Ha’penny Bridge to Stoneybatter, 20.
City-centre traffic is bad and a bus across town at five in the afternoon loses to a person on foot.
The Leap Card
The transport card, valid on Luas, DART, Dublin Bus, commuter rail and the airport bus, and considerably cheaper than cash fares.
The Leap Visitor Card gives unlimited travel for 1, 3 or 7 days including the Airlink from the airport, and usually pays for itself on a short trip.
Contactless bank cards work on the Luas and DART but not on Dublin Bus, which catches people out.
Luas
Two tram lines. The Green Line runs north–south through the centre via O’Connell Street, Trinity and St Stephen’s Green. The Red Line runs east–west via the Docklands, the north quays, Smithfield and Heuston Station.
Validate your Leap Card on the platform pole before boarding. Inspectors are common.
DART
The coastal railway, and the best thing in the system — Howth in 30 minutes, Dún Laoghaire in 20, Malahide in 25. The coastal stretches are genuinely scenic.
Buses
Extensive, and how you reach Phoenix Park, Kilmainham and Glasnevin. The network was redesigned under BusConnects with lettered spine routes; use a journey planner rather than the map.
Stops are request stops — flag the bus down or it will not stop.
Cycling and taxis
Dublinbikes covers the centre densely and a three-day ticket is cheap. The canal and coastal routes are the pleasant rides.
Taxis are metered and plentiful; FreeNow is the app locals use.
Do not hire a car for a city stay. Parking is scarce and expensive and everything is walkable. If you do drive, the M50 has a barrier-free toll that must be paid online by 8pm the following day.
The longer version is in getting around Dublin.