The 39 Steps.
The 39 Steps was a 1959 British thriller film directed by Ralph Thomas and starring Kenneth More and Taina Elg. It was a remake of the 1935 Alfred Hitchcock film based on the 1915 novel The Thirty-Nine Steps by John Buchan. Interior filming took place primarily at Pinewood Studios, with extensive location filming in Scotland, This article shows several locations in and around The Trossachs.
My thanks especially the team on the Callander Past and Present Facebook page for permission to use images.
Glenkirk House was in fact the Altskeith Hotel on the banks of Loch Ard. 
Richard Hannay meets with Professor Logan, the man with the missing finger in the Altskeith Hotel. 
A scene showing a car going over a bridge was filmed at the Teapot. 
Filming of the 39 Steps at Brig O’Turk. 
Filming at Brig O’Turk. 
Police Car in scene at Brig O’Turk at ” The Gallows inn.”
The following are some more scenes from in and around the Trossachs.
St Catherine’s School which is Tigh Mhor. 
Richard Hannay hiding–filmed at Tigh Mhor. 
River Balvaig at Balquidder 
On the shore of Loch Lubnaig. 
The escapee near Loch Lubnaig. 
Kathleen from Callander who was the stand-in for Taina Elg.
Some more interesting information in this slide.
James Kennedy April 2021.