Imagine we are playing with toy cars, and we have a sandy area. If we want to make a road in the sand, we can push some of the sand from the middle to the sides. This makes the road higher than the ground next to it.
Now, imagine some people were playing with toy cars a long time ago, and they made a road like that. But over time, the wind blew sand and dirt onto the road, and plants and grass grew on the sides. The plants and grass made the sides taller and the road lower.
This is what a sunken lane is. It is an old road that was made by people a long time ago, but it got lower because of nature. It's like a little valley or trench that cars or people can still go through, but they have to go down into it and then back up.
Some sunken lanes are very old, and people can go on walks or hikes to see them. They are interesting because they are like a little piece of history that is still there, even after a long time.