Cardiff (Welsh: Caerdydd) is the capital of Wales.
When you're coming to Cardiff and get dropped off at a motorway junction on the M4 it's best to go for J32 then walk about half a mile down the A4054 towards Whitchurch and you'll find a train station where you can get to the centre of Cardiff for about £2.
Direction: All directions
M4 Motorway East via A48
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Walk out of Cardiff along Newport Road, or take the North-East bound bus to Penylan. There is a nice spot by a car shop just down from the bus shop, with a lay-by where cars can easily stop. It's a wide road with busy traffic, so you'll be easily noticeable.
The road will take you to the A48, which leads to the M4 going East. Plenty of people in that part of Cardiff will be going this way to get onto the motorway.
M4 Motorway East
Alternatively, it may make more sense just to take a bus to the Cardiff Gate Services. In Sept. 2015, we hitched using the option above, waited about an hour, and then just got a ride to the services. Turned up to be very helpful as we got a ride all the way up to Oxford, BUT, there is a bus that runs right there. Take the X59 to Malthouse Avenue, BP Petrol Station, Pontprennau. Not sure the fare but don't think it's much more than the bus that runs to Penylan.
Another option, if you're already on the north side of Cardiff is to walk to the Coryton roundabout and find the exit for M4 East. It's not the best place to stop, but [User:Blanky|Blanky] has managed to get picked up, although there was almost a car crash. You may be better off thumbing or using a sign at one of the entrances to the roundabout, possibly from Merthyr Tydfil where there are traffic lights. Those who attempt this should be informed that the roundabout is quite complex.
Direction: Swansea, North Wales
M4 Motorway West
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Get the number 57 or 58 bus to Pontprennau. Get off at ASDA, walk to the roundabout, turn left, walk up the dual carridgeway to the main roundabout and you'll be able to hitch on the exit roads to the motorway, east or west.
There are 2 (more or less) permanent squats/social spaces in Cardiff, called Wells Hotel (77 Craddock Str) and the Red and Black Umbrella (57 Clifton Str).