I suppose someone could run a charter from Wick to Penzance, wonder who would be up for that!
It has been done, by the Wirral Railway Circle on 24-27 May 1974. Details are on Six Bells Junction.
Through the 1980s F&W (predecessors of Pathfinder) ran a number of weekend railtours from the West Country to Scotland called Skirl o'the Pipes.
About 30 years ago the NENTA summer weekend from East Anglia to Scotland was an annual fixture, doing Mallaig in 1990, Kyle in 1991 and Thurso in 1992.
Saturday night engineering work spreading like Japanese Knotweed put a stop to trains such as these.
A 'Cathedral Line' service? Works for me.
Go back in time and there were through trains between Norwich and Newcastle that passed by the cathedrals of Norwich, Ely, Lincoln, York and Durham. By the 1980s the train was still running on summer Saturdays, and, though it lost Lincoln, it gained Peterborough.