Off the beaten track

[gtsl]

Morning, looking for a bit of knowledge here. A Friend and I looking to explore a bit further on our bikes. When driving through the Highlands we noticed a lot of gravel tracks leading around and over the mountains and hills. are there any that can be ridden for a good distance? I know there are no green lanes in Scotland but not sure the rules on these tracks. Would be good to explore and enjoy the countryside a bit further than normal.