Budapest’s transport is run by BKK: four metro lines, an extensive tram network, buses, trolleybuses, the HÉV suburban railway, and boats.
Metro. M1 (yellow, 1896, under Andrássy út), M2 (red, east–west, crosses the river), M3 (blue, north–south through Pest), M4 (green, newest). All four meet at Deák Ferenc tér.
Trams. These do most of the work. Trams 4 and 6 run the Grand Boulevard around the clock. Tram 2 runs the Pest embankment past the Parliament and is worth riding for its own sake.
Tickets. A single is valid for one journey on one vehicle. Buy a 24-, 72-hour or weekly travelcard instead — it covers everything within the city and removes the problem entirely.
Validation. Single tickets must be validated before travel, in the machines at metro entrances or on board trams and buses. Inspectors work in pairs, are frequently at metro exits, fine on the spot, and make no allowance for confused visitors. This is the most common bad experience people have here.
Taxis. Fares are regulated and identical across licensed companies, so there is nothing to shop around for. Cabs are yellow with a door number. Uber does not operate in Hungary; Bolt does.
Airport. No rail link. Bus 100E runs direct to Deák Ferenc tér and needs its own ticket, not a travelcard. Bus 200E plus metro M3 is slower and covered by ordinary tickets.
For the full detail, see Getting Around Budapest.