Mull is an island that can only be accessed by ferry. The page Getting there describes the three ferry options: Oban to Craignure, Lochaline to Fishnish and Kilchoan to Tobermory. The fastest option, unless you travel from the North of Scotland is to take the ferry from Oban to Craignure operated by Caledonian MacBrayne. Booking early is essential.
From Craignure, follow the signs to Tobermory (A849 which becomes A848 after Salen). Shortly after passing the “Welcome to Tobermory” sign, you will get to a roundabout. Follow the route in blue on the map below (copyright Google).
Roundabout at the entrance to Tobermory
Follow the road down the hill (second exit)
Drive past the distillery
Drive along the Main Street
Until you get to the Back Bray. Then turn left
Drive up the steep road
Bear right and stay on the Back Brae
Bear right. The street becomes Erray Road
Just as you Drive past Raeric road on your left, An Cala appears on your right.
Turn right
And then turn left left in the driveway.
Park your car(s) in front of the garage
The key lock-box is mounted on the left hand side of the entrance door
