The Memorial Chapel at the University of Glasgow can, in normal times, be visited every weekday from 9 till 5 and when I visited I had the whole place to myself for a few minutes before more people came in. It was completed in 1929 to serve as a memorial for members of the university who had died in both World Wars and interestingly both Protestant, Catholic and humanist marriages can take place there.
The chapel was designed by John James Burnet around 1913 but building was delayed by the outbreak of the First World War. It’s not surprisingly a small building but a lovely space nonetheless and has some wonderful stained glass windows designed and made by Douglas Strachan. He died before he could install all the windows he’d designed, so these were worked on by others from the 1950s to the 1960s.
You can find some more photos here.