Skavsta Airport (NYO) is located about 100 kilometres (62 miles) southwest of Stockholm, just outside the city of Nyköping.
The airport is served by low cost airlines such as Ryanair and Wizzair.
When you arrive, you have a number of different ways to transfer from the airport to central Stockholm. Here are the options.
Your best option is to travel on the Flygbussarna, an express bus that runs between Skavsta and Stockholm (Cityterminalen). The bus schedules are adapted to flight departures and arrivals, and the trip takes approximately 80 minutes. An adult ticket costs 159 SEK one way, and 285 SEK round trip (slightly less on the app/online).
Buy the ticket on the Flygbussarna website or app, at the airport counter (open Monday to Saturday from 7am to 1am, and Sunday from 8am to 1am), using the ticket machines located by the bus stop, or on board with your debit/credit card.
The train is not a great option to get to Stockholm city centre, since the station is located in Nyköping, about 7 kilometres (4 miles) from the airport. In any case, these are the directions: take local bus 515 to Nyköping Station and from there catch the train to Stockholm. Check out the SJ timetables.
A taxi ride between Skavsta and central Stockholm can be quite expensive. The journey takes about 70 minutes, and the price varies between 1,500 and 2,000 SEK.