NB Sat Nav will not take you to Cardross house but rather centre of postcode, directions below will help address this

From Stirling & the East:
Leave M9 motorway at Junction 10. Turn onto the A84 towards Doune & Callander. After approximately six miles turn left onto the B8075 to Gargunnock. At the T-Junction turn right onto the A811 signposted to Erskine Bridge. Continue to Arnprior, turn right onto the B8034 towards Port of Menteith, after two miles you will cross a hump backed bridge, the drive to Cardross House is the next turning on the right (you will see a yellow gatehouse and cattle grid and ‘Cardross’ on the pillar)

From Glasgow:
Follow A82 signposted to Dumbarton, Balloch & Loch Lomond until the end of the dual carriageway. Turn right onto the A811until you pass through Buchlyvie. Take the next left onto the B8034 towards Port of Menteith, after two miles you will cross a hump backed bridge, the drive to Cardross House is the next turning on the right (you will see a yellow gatehouse and cattle grid and ‘Cardross’ on the pillar