Another of the great offerings by the National Library of Scotland. The 'Digital Gallery' is the name for a wide range of different digital collections. Of course, one of the great things about digital collections is that they're accessible online, so although going to the National Library of Scotland in Edinburgh is a great experience, you can still access all this wonderful stuff from your own online device.
The one of overwhelming interest to Scottish musicians is their Special Collections of Printed Music
Two big collections of old sheet music have been professionally digitized. One collection belonged to Scottish music collector John Glen, and the other to Alexander Wood Inglis. There are hundreds of digitized scores of traditional music repertoire.
This is more than worth a look - it's essential reading!