The Somerville Armory is at 191 Highland Avenue.

There is parking behind the Armory, and if that lot is full, there are two nearby lots:

112 Central Street, and 75 Belmont Street, both in Somerville.

You can take the Red Line to Davis Square, and walk (about a mile) along Highland Avenue.

And there are two bus lines that go right by the Armory:
   The 88 (Clarendon, Davis, Lechmere)
   The 90 (Davis, Sullivan, Assembly)