Chesapeake Bay Bridge-Tunnel

A 28 km crossing of the mouth of Chesapeake Bay that alternates between low trestle bridges and two mile-long tunnels bored beneath the shipping channels, so warships and container traffic can pass overhead. When it opened in 1964 it was named one of the Seven Engineering Wonders of the Modern World.

Driving it is genuinely strange: for twenty minutes there is no land in any direction, just two lanes of concrete a few metres above open water, gulls, freighters and — often — dolphins working the surface below. Then the road tilts down and disappears under the sea. Four artificial islands were built from a million tonnes of rock to make the tunnel portals. Seven men died during construction.

Practical: a toll road, currently around $20 each way, cash or card. It replaces a 153 km detour around the top of the bay. High winds close it to high-sided vehicles and occasionally to everyone, so check the status in bad weather. There is a scenic overlook at the northern end and a rest area on one of the islands.