The answer
There is no train at Dublin Airport — anyone selling you a "train ticket" is reselling a bus seat at a markup. Walk out to the coach zones: Aircoach 700 — €10, every 15 min, runs 24/7, drops you on O'Connell Street.
Book on the Aircoach site a few days ahead and the same seat is from €6. Kids 4–13: €5.50.
Tight budget? Dublin Bus route 16 — €2.00 with a Leap card (buy one from the arrivals vending machine). Cash works but it's coins only, exact fare, no change given. 60–80 min.
⚠️ The traps (walk past these)
The exact-change bus trap
Regular Dublin Bus fares are coins only — no notes, no cards at the door on older buses, and no change given. Pay €3 in coins for a €2.60 fare and you've donated 40c. Tourists feed the machine notes' worth of coins every day.
Do this: buy a Leap card at the arrivals vending machine (€2 fare instead of €2.60) — or take Aircoach, which takes cards.
Airport ATMs — the €6-on-€20 fee
The standalone ATMs in arrivals charge around €6 to withdraw €20, plus a terrible exchange rate if you let the machine convert. Dublin is nearly cashless — pubs, buses (Leap), and taxis all take card.
Do this: don't withdraw here. Pay by card, and if you need cash, use a bank ATM in the city.
"Train to the city?" offers
Dublin Airport has no rail link at all — no DART, no Luas, no metro (MetroLink is still unbuilt). Anyone selling "train tickets" or "express rail" transfers is reselling you a coach seat with a markup.
Do this: buy coach tickets from the Aircoach/Dublin Express sites or at the stop — never from a reseller.
The midnight meter shock
The taxi meter switches tariffs by law: premium rate 20:00–08:00, and a special higher rate 00:00–04:00 on weekends — plus the €3.80 M50 toll gets added on top. The same trip can cost €29 at 2pm and €50 at 2am.
Do this: late arrival? Pre-book a fixed-price transfer, or take the 24/7 Aircoach.