By bus
National Express (http://www.nationalexpres...) operate regular services to and from most other major cities in Britain with Cardiff Central bus station, which is in the forecourt of Central railway station, making it quite easy to switch between train and bus. In addition, MegaBus offer a regular and very cheap service to London and departs from near Cardiff Castle. Cardiff is about 3 hours, depending on traffic, from London.
By train
Wikitravel has a guide to Rail travel in the United Kingdom.
Cardiff Central railway station is a major hub for many services and is in an ideal location being very close to the main city centre attractions and is in close proximity to Cardiff Bay. Arriva Trains Wales (http://www.arrivatrainswa...) operate the vast majority of inter-Wales services with regular departures from Cardiff Central to the South Wales Valleys, Swansea, and a frequent service to North Wales. They also operate regularly to Manchester and Birmingham making Cardiff ideal to visit via rail. All inter-city travel is via Cardiff Central while Cardiff Queen Street station near the eastern end of the city centre is the hub for Cardiff's Valley Lines services, connecting the centre of the city with the suburbs and commuter towns. Both stations are controlled by ticket barriers, so you will need a ticket to enter or leave the platforms. Ticket machines are in the entrance of both stations and in Central station there are many maps that will help you plan your journey.
Cardiff Central is two hours from London Paddington by train, however some may take longer with more stops. Trains depart half hourly during the day and are operated by First Great Western (http://www.firstgreatwest...). These services also continue hourly to Swansea. First Great Western run a service from Cardiff to Portsmouth Harbour via Newport, Bristol, Bath and Southampton.
Rail service provides quick and easy links to other interesting areas such as the Vale of Glamorgan and West Wales, making Cardiff a pleasant and cheaper place to use as a home base while exploring the surrounding areas.
The city itself has around 22 train stations within its boundaries, with travel to North Cardiff especially accessible, Travel to tourist attractions such as Cardiff Bay, Castell Coch and Barry Island can be easily and cost effectively reached by train or bus.
By plane
The main airport is Cardiff International Airport. This is the only major airport in Wales and is situated some 12 miles to the south-west of the city in the Vale of Glamorgan. The airport is served by a number of airlines including Flybe (http://www.Flybe.co.uk), KLM (http://www.KLM.com), Thomsonfly (http://www.Thomsonfly.co.uk) and Skybus (http://www.skybus.co.uk). KLM provide worldwide links to Cardiff via Schipol Amsterdam, NL. Domestic services operate daily to Anglesey, Belfast, Newcastle, Newquay, Jersey, Glasgow and Edinburgh. As for European routes, Amsterdam, Paris, Madrid, Dublin, and many other holiday routes such as Faro, Palma de Mallorca and Alicante, operate daily.
By car
From London and the South East of England, Cardiff is most swiftly reached by taking the M4 motorway west across the Severn Bridge and into Wales. Journey times from Central London to Cardiff are usually 3 hours, although visitors from Heathrow could shave up to an hour off this time. Don't forget the bridge charges a toll to cross cash only! See (http://www.severnbridge.c...) for up-to-date information on toll charges. The M4 is also the main artery linking Cardiff with West Wales including Swansea, while the A470 road mainly links Cardiff with the South Wales Valleys. Traveling from North or Central England and Scotland the M50 links the M5 motorway with Wales and continues down to south Wales eventually linking with the M4.Cardiff's junctions are 29 - 34 inclusive.
Within Cardiff, it is cheaper to find a train station and continue onto the city centre via train, as car parking within the city although plentiful, can be expensive. Getting around the city by car is straightforward, even within the city centre, it is quite easy moving around; although, it's best to restrict entering the city centre area during off-peak times as congestion can occur at rush hour like any city. Generally though, the city centre is pretty compact and its much easier and cheaper to move around on foot.
See (http://www.cardiff.gov.uk...) for a list of Cardiff City Council operated car parks.