Well kiddo, the Orkney Tunnel is a big road that goes under the water to connect two places called Mainland Orkney and Hoy in Scotland. It's like a secret tunnel that goes underwater instead of over the top like a bridge.
You know how you can make a tunnel with your hands by connecting your fingers together? It's kind of like that, but huge!
The Orkney Tunnel is made of really strong materials like concrete and steel so it can hold up the weight of all the cars and trucks that go through it. It's also specially designed to let water flow through it, so it doesn't flood or break.
People use this tunnel to go from one place to another without having to go all the way around the water, which can take a long time. It makes traveling much easier and faster.