Can I bring a drone to the Scottish Highlands ?

Field outdoor is okay, castle is not.

Of course you can bring it. Scenic areas with flight restrictions will have signs.

There is a no-fly reminder at the entrance. Just fly quietly as long as you don't see any staff.

I saw a young foreigner use it when the steam train came at Glencoe Bridge, which I didn't see anywhere else.

Sure, I've flown drones over Skye, the three English Estates, and the White Cliffs of the South. No problem in less populated areas.