Map (pdf) from the Hotel Dieci to the Department of Physics

From the railway stations Milano Centrale and Milano Cadorna:

From Milano Centrale (or from Milano Cadorna) take the green subway (=line number 2), direction "Gessate/Cologno". (Tickets are again available at the newsdealers).
Get off at "Piola".
From there (see also the map above) follow the flux of students (which is always nonvanishing) to arrive on "Piazza Leonardo da Vinci" (about 100-200 meters from the subway station). Cross the whole piazza, leaving the Politecnico to your left. You arrive on Via Celoria. Turn left and go along Via Celoria, up to the traffic lights. The main entrance of the Physics Department, on Via Celoria 16, is immediately after the traffic lights on the right hand side.

From Milan Malpensa airport:

Take either the Malpensa express to arrive at Milano Cadorna (45 minutes) or the bus to arrive at the Milano Centrale railway stations.
From there, follow the instructions here above.

From Milan Linate airport:

Take the bus number 73, direction "San Babila". (Bus tickets are available at the newsdealers).
Get off the bus at "Corsica Campania" (8th stop, ask driver or other passengers to get the right stop).
Now take the bus number 93 (you do not need to buy a new ticket), direction "Loreto" and get off at "Ponzio Celoria" (6th stop).
Enter the Physics Department through the main entrance on Via Celoria 16.

From Orio al Serio (BG) airport:

Regular buses connect the airport to the nearest train station, from where trains leave every 30 minutes in the direction of the Milano Centrale, Milano Porta Garibaldi and Milano Lambrate (the nearest one to the Physics Deptartment) stations. The journey takes approximately one hour.
There are also several buses in operation between Orio al Serio and Milano Centrale (details at Autostradale web site) or Milano Lambrate (details at Zani viaggi web site) stations.
Otherwise Milan is accessible by car in about 40 minutes.