Okay kiddo, so Stonehenge is a very old and mysterious place in England where big rocks were put together in a certain way a long, long time ago. And now, people go there to visit and learn about history.
But the problem is that there is a road that goes right next to Stonehenge and it has a lot of traffic on it. This can be dangerous for people who want to visit Stonehenge. So, some grown-ups have come up with a plan to build a tunnel under the ground to allow the road to go under the rocks in a safe way.
This way, people who want to visit Stonehenge won't have to worry about cars and trucks going by too fast. And it will help protect the ancient rocks too, so they can stay there for even longer and people can keep learning about them.