Nationals of the United States, Canada, and Australia do not need to apply for a tourist visa to enter Wales. Six-month visas are granted on arrival, free of charge. These rules also apply to citizens of most South American and Caribbean countries, and of Japan. More information on UK visas can be found via the UK Border Agency.
Health and Safety
On the whole, Wales is one of the safest places in the UK to visit and crimes committed against travelers are fairly rare; however, it is always worth maintaining a degree of common sense. Certain areas of Cardiff and Swansea should be avoided especially after dark, although you are unlikely to end up in these places as a tourist. It is also a good idea to keep an eye on your belongings and refrain from having valuables in easily accessible pockets when on public transportation or in crowded areas. While cases of mugging and pick pocketing are fairly low, there is no reason to tempt fate.
Emergency treatment is available free of charge to US citizens and nationals of EEA countries. However, visitors are always advised to take out travel insurance to cover other unexpected circumstances. When hiking, always let others know your route in advance as rapidly changing weather can pose a danger.