Cardiff in making iron and later steel, brought to the sea by packhorse from Merthyr Tydfil. This was first achieved by the construction of a long canal from Merthyr (510 feet above sea-level) to the Taff Estuary at Cardiff. Eventually the Taff Vale Railway replaced the canal barges and massive marshalling yards sprang up as new docks were developed in Cardiff – all prompted by the soaring worldwide demand for coal from the South Wales valleys. At its peak, Cardiff's port area, known as Tiger Bay, became the busiest port in the world and – for some time – the world's
Cardiff Bay of Torchwood entitled "Children Of Earth", Cardiff Bay was the centre of a bomb explosion, destroying the Torchwood Hub and Cardiff Bay. Roald Dahl Plass features prominently. The "Doctor Who" episode "The Runaway Bride" made use of office buildings in Cardiff Bay. Cardiff Bay railway station is northeast of Mermaid Quay and is served by shuttle services to Cardiff Queen Street railway station. Cardiff Bus operates the following services to the bay: The bay lies off the A4232 before the Butetown tunnels and is linked to the city centre by Lloyd George Avenue, Bute Street and the Central Link Road.