Sounds a bit strange I know, but if you really want to you can! Since the launch back in 2001 more than 10 million articles (in 253 languages) have been published. 25% of these are written in English.
The content is free and available to anyone under the GNU Free Documentation License. However, this doesn’t mean you can start running your own Wikipedia but you may download and use the information for your own personal/private use.
From time to time the complete database is dumped as static HTML files, the last available release was “dumped” in June earlier this year. You will need something like 7-zip to unpack the files which is available from this location. The English version, a massive 14GB download is found here (at the bottom).
You might ask yourself WHY on earth you would want to download it?! Well, to be honest I really don’t know. But in case you are going somewhere without an Internet connection or similar it could possibly prove useful… 🙂