First step, check http://www.downforeveryoneorjustme.com/ and make sure the site is online.
If the site is online, the internet connection or wifi you are using may have blocked the website. Or the website server may have blocked the country you are currently in to prevent spam, hacking or even as an agreement with that country. There are some options to try and get around this:
- Use a Personal VPN like hotspotsheild. This is the simplest option. I like to keep it on my computer because there’s no guarantee you can get to their site to download it while you are in another country. http://hotspotshield.com/
- Use and Onion Router like Tor. This option is more complicated to use but works well. https://www.torproject.org/download/download.html.en
Both options will slow down the websites you are trying to access so be patient.
If your planning a trip to the following countries, you should download the above before leaving the US: China, Cuba, Iran, North Korea, Saudi Arabia, Vietnam.
For a full and current list of countries with strict Internet Censorship, visit:
https://secure.wikimedia.org/wikipedia/en/wiki/Internet_censorship#Around_the_world