The On Inn will be LA Bar in Årsta, Hjälmarsvägen 2. It's about 100m from Årsta Torg. Usual half-arrows will be marked from the nearest tram station, which is Valla Torg. Easiest way from Centralen is the pendeltåg to Årstaberg and then change. But you can also get the green line to Gullmansplan or the red line to Liljeholmen and change