Metro red line 13 to (T) Gärdet (GÄR) in the train towards Ropsten (ROS) in the front carriage if you come from the city and then down on the road downwards to the left and then across the road after turning right going downwards to the On-Inn Pizzeria Värtan down by Värtahamnen at Södra KAJEN 37 below Scandic Ariadne,Tallink and it is very close to the water of Värtahamnen...
The On-Inn is about 600 meters from (T) Gärdet (the north exit closest to Ropsten) and it is easiest/shortest/fastest to get there if you you go across the railway tracks on the bridge in front of Scandic Ariadne
through the tunnel going to Scandic Ariadne to the right of "Värtaterminalen" and go
down into Scandic Ariadne and then continue forward through it and there go down to
the left on the stairs going down and then walk about two meters to the left...
(Going down,down,down...)