Travel by car or bus via the A82/A83 to Inveraray and onwards to Lochgilphead and then onto Kilmartin and nearby Crinan.
Alternatively, travel via the A85 and then south after Dalmally to Inveraray, and onwards.
Another route is via Oban along the A816 southwards to Kilmartin.
Check out West Coast Motors for more details on all of the above.
You can also catch Calmac ferry connections from Arran or Cowal to Kintyre and then travel northwards to the Kilmartin Glen.