From Sacramento/San Francisco

I-80 to
HWY 49 to
Grass Valley / Colfax Hwy 174 Exit
Left off ramp on to South Auburn St.
Left on West Main St
over the hill to #816 West Main St.
 

From Reno

I-80 to
HWY 20 to
Grass Valley / Colfax Hwy 174 Exit
Right off ramp on to Bennett Street.
Left on Main Street
over the hill to #816 West Main St.

Yes you can walk to Old Downtown Grass Valley, it is about 3 blocks away