Piešťany sits on the main rail corridor between Bratislava, Trnava, Trenčín, and Žilina, so the train is usually the easiest way in. The station is west of the centre; taxis and local buses cover the short hop to the spa quarter, but light travellers can walk it.
By road, the D1 motorway passes close to town. That makes Piešťany an easy stop on a Slovak road trip, especially if you are moving between western Slovakia and the Tatras.