How grand a dream was it? It started off with people in Bristol wanting a railway to London 190km (120 miles) away for carrying goods quickly between these two cities. Many things had to happen before they could get their railway. One of them was finding someone to build it.
They chose Isambard Kingdom Brunel. He was already famous for his bridges and tunnels. Since the route for the railway would need these, he seemed the ideal choice. He then made the dream a bigger one.