I'm staying in Arese on our way to Tuscany late May....mainly because its just off the A8 Autostrada which is our route anyway.
But have read in a few places the Museum is closed and has been since 2011 alas.......
"The museum is located in Arese (MI), viale Alfa Romeo, at Centro Direzionale Alfa Romeo.
By car, take the SS 233 Milan-Varese highway or the Milano-Laghi Motorway A8-A9 - Arese exit.
For information: tel. +39 02 444 294 21; +39 02 444 293 22
The Alfa Romeo Museum is closed until further notice for maintenance. We apologize for any inconvenience"