Leave motorway at Junction 10 and come in towards the castle and follow signs for Loch Lomond / A811 to Drymen, Erskine Bridge and Loch Lomond. Stay on A811, straight over roundabout at Kippen/Thornhill junction, go through Arnprior and Buchlyvie. 2 mile after Buchlyvie take turning on left to Balfron (A875).
From Glasgow Airport
Take M8 toward Glasgow, leave at Junction 25 to Clyde Tunnel, and follow signs for north and Aberfoyle (A81). When you get to Canniesburn Toll roundabout take second left to Milngavie (not Drymen A809). Stay on A81 through Milngavie, Strathblane, Blanefield until you pass Glengoyne whisky distillery on right. Take turning on right after the distillery to Killearn. Go through Killearn, Boqhuan and into Balfron.
From Edinburgh Airport
Follow M9 to Stirling, leave at Junction 10 and then follow directions from Stirling as above.