Hello !

To go from Milan to St.moritz, the quickest way would via Chiavenna (and then take a Bus to St-Moritz) or via Bellinzona (and then take a bus to Thusis) however these two are not included in your Interrail, if you want to be faster, you can still buy a ticket on www.sbb.ch/en for this route. With an interrail, the quickest way is to go via Tirano in Italy and then take the Bernina line (which is also a Unesco site) to St. Moritz. In this case the pass would be valid from TIrano onwards and you would have to buy a ticket from Milan to Tirano separetely (it costs 12.50 euros) which you can buy on this website: IT - Trenitalia

Unfortunately, due to track works, this summer the line between Milano and Tirano is partially closed, so you will have to change in Colico and take a replacement bus to Tirano (which makes the journey longer).

In the case of your trip from Lugano to Milano, the interrail one country pass of switzerland is valid until the border town of Chiasso, from then onwards you will have to buy a separate ticket wich you can find on the aforementioned Trenitalia website.

The validity of the One Country Pass Switzerland is detailed in the map found on this page: https://www.interrail.eu/en/plan-your-trip/tips-and-tricks/trains-europe/trains-country/trains-switzerland (2nd alinea in the white window, “Click here to download...”

Interrail One Country Switzerland will be valid until Domodossola, Luino, Chiasso, Tirano,…

Shortest way to Milano is via a bus from St. Moritz to Chiavenna (this bus is not included in the pass).

Check www.sbb.ch/en for detailed timetables, use settings and deselect bus if you only want to use trains (and replacement busses). But’s that easily +3h longer.

If we are taking the train from Milano to Chiavenna and taking a bus from Chiavenna to St.Moritz, Where do we have to buy additional ticket to, when we are traveling with the one country pass Switzerland? I looked up the map of Switzerland, but it is a but unclear 

Thank you so much! 

You'd have to buy everything then as buses are not included nor trains in Italy with a One-country pass Switzerland.

Alternatively buy a ticket to Tirano for 12€ (usually fully by train but partially replaced by buses until mid-September). Then your pass is valid on RhB trains.