Not only is there a light at the end of the tunnel, but there's also a light at the beginning of the tunnel. Make sure you know which way you're facing.
All bridges go two ways.
There are lights at both ends of a tunnel. You can put one-way signs and tire treadles on the road. You can keep your eyes peeled on the light ahead of you. But you can always return. Whether you build a bridge to another land mass or to a new millennium, there is always a way to go back.